A story came out some time ago that, when the app-using habits of iPhone users was studied, it turns out that most downloaded apps don't get used much: about 4 of 5 people who downloaded a free app never used it again after that first day, and nearly 2 in 3 who paid to download an app did the same.
My experience: Yeah, that sounds about right.
Here's the list of apps that have existed on my iPhone at one time or another, organized by usage pattern. Note, this does not include the apps that came with the iPhone, which can't be deleted (but can be moved to 'back pages' if you're not making regular use of them).
Not currently on the phone:
Diceshaker (free) - A cool-looking die roller app, I picked it up with the thought of using it to make my D&D die rolls electronically. It had two significant flaws: first, you could only roll one die with it. Second, the die you defined in the setup (you could define a die with any number of 'sides') would never actually roll its maximum value.
It did make for an interesting psychological experiment -- I was in my last days of playing D&D Minis when I grabbed the app, and asked a few opponents if they'd let me use the Diceshaker app instead of rolling a physical d20. Every one refused, and every one suggested that they'd be unable to tell if the program was 'honest'. I knew the program wasn't 'honest', but it was flawed in a way that would harm me (since I couldn't roll a 20, I'd never get a critical hit or automatic success). Still, nobody even considered that as an option.
Eventually replaced by Dicenomicon (see below).
GeoHash (free) - A free app inspired by this XKCD webcomic. The original app was updated after the algorithm chosen by the programmer couldn't handle the Dow falling below 10,000.
Downloaded because I thought it was cool. Removed to make space for apps I'd actually use. It might go back onto the phone, if I found someone like Randall Munroe to go on adventures with. (Though that's really just an excuse, honestly.)
MySpace Mobile (free) - Originally downloaded about the same time as Facebook (see below), because I knew people on both services. Now that everyone I knew on MySpace has migrated to Facebook, I don't bother keeping up with the MySpace part of the interwebs anymore.
Obama '08 (free) - Originally downloaded to piss off my right-wing gaming cohort Mark, this turned out to be an extremely well-done app, combining contact information, web-based data (position papers, mostly), and other features into a seamless whole (at least, as far as I explored it).
Removed after Obama won the election, because we live in a representative democracy, and the guys I voted for, who largely agree with my views on things, won.
Currently on phone - not used in months or not sure when last used:
Google Mobile App (free) - It's not that the Google Mobile App is a bad app; it's just that most of what I do with it is more easily accessed in other apps on the iPhone -- for instance, Mobile Safari has a Google search bar on the browser. Likewise, the Maps app has a search feature that doesn't require you to 'hitch' over from the Google Mobile App.
If I made more use of Google Apps, and specifically the Google Apps set up for the use of our local gaming group, I'd probably get more use out of the Google Mobile App. At the moment, though, it would be the next app to go if I had to make room.
SportsTap (free) - I used this app frequently during the 2008 baseball season to grab scores, check stat lines, and track the pennant chase between the Twins and White Sox. Since then, I haven't had much call to use it, since I'm not a huge Vikings or Timberwolves fan anymore. We'll see if the new baseball season causes me to increase my usage of the app again.
Remote (free) - This Apple app is still on the phone because of the potential of being able to use it to remotely control my MacBook or MacMini if needed. To this point, it hasn't really been needed.
eReader (free) - I like the idea of using my iPhone as an electronic book reader; this is one of three reading-type apps on the phone right now. I originally chose eReader because of its library of free public domain texts; I downloaded and read Sir Arthur Conan Doyle's 'A Study in Scarlet', and haven't really used it since.
WarcraftStat (free) - An app to check the status of servers in World of Warcraft. Not really used much, because it's just as easy to check online when I'm actually at my computer and considering playing. It's still here, because I think of it as a matched set with the Warcraft Characters app, though as far as I can tell they were not coded by the same programmer.
Currently on phone - used within past month, but not regularly:
Warcraft Characters (free) - An iPhone interface to an online database that mirrors World of Warcraft character data. I haven't spent a lot of time in WoW of late, so this pair of apps (Characters and Stat) might go if I decide to give up my subscription again. (Why I feel the need to drop my subscription almost immediately after purchasing an update to the game client is a topic worthy of its own past, someday.)
Lightsaber Unleashed (free) - The first app I ever downloaded for the iPhone, back before LucasArts either purchased or claimed IP ownership of the app and re-vamped it as a tool to sell 'The Force Unleashed'. Still cool to swing the phone around and hear the lightsaber sounds, though.
Careerbuilder.com Jobs (free) - A great idea for an app, but the combination of a crappy job market coinciding with the recession, plus some significant limitations in the app (you can't simply browse job listings in your area - you're required to enter a keyword to search on if you want to search the job listings) have kept me looking for a replacement for some time. No luck yet.
Dicenomicon ($3.99) - A far superior dice rolling app to Diceshaker. Gives the ability to roll multiple dice, to group dice in multiple 'pools' (so you can roll all the dice you need to create a D&D character with one shake), and the ability to program specific types and numbers of dice to match just about any game system. The 'help' screens are incredibly helpful, especially the section for specific game systems which contains formulas for use with D&D, AD&D, Storyteller (Vampire and similar games), and the HERO system, plus others.
Absolutely worth the money in terms of functionality; only problem is, like Diceshaker above, most DM/GMs don't want you rolling electronic dice, assuming that you've skewed the program somehow to cheat. Ah, well, I guess it's only human nature.
Shakespeare (free) - This app is used infrequently only because, even with my theatrical background, I don't have the need to consult the complete works of William Shakespeare on a regular basis. Still very cool, though, especially the program icon.
Bonus points: With the addition of a Search feature, this app becomes a great companion for the Canadian television series 'Slings & Arrows'.
AP Mobile News (free) - This used to be an app I'd access multiple times per day, during the election season. As time has gone on, though, the people coding this app have seen fit to try to make it more 'bells and whistles-y', including (most depressingly) banner ads to help pay for the development cost. I loved this app when it was a simple, no-frills interface to the day's news; every update gets me closer and closer to trying to hunt up a new app to capture that old minimalist feeling.
Stanza (free) - Another e-reader application, this one came recommended along with a promotional set of e-book downloads, one of which was from a writer I knew and admired - Laurie Notaro. Since that first e-book, I haven't been motivated to go pay for another.
Currently on phone - being used regularly, but too new to tell if it'll last:
CBS TV.com (free) - Grabbed almost entirely based on the reports in the Mac press that the original Star Trek series could be accessed via the app. There are a few other CBS shows that I might follow (How I Met Your Mother, Big Bang Theory) if I got into the habit, but since I'm long out of the habit of watching actual television, it's hard to tell how eager I'll be to consume it on (to borrow a phrase from Yahtzee Croshaw) 'teeny-weeny eyestrain-o-vision'.
iBlogger ($0.99) - I've made a couple of short posts to this blog from iBlogger, but I can already tell that my preferred long-winded style including the occasional hyperlink won't translate well from the iPhone's tiny keyboard. I now understand why Twitter clients for the iPhone are so popular.
The Weather Channel Weather App (free) - This one probably has the best chance to stick around -- the app is far more detailed than the included Weather app, and can provide much more in-depth information about upcoming weather conditions. It would be slightly more useful if I were still taking the bus to work, as it would help me to always have an umbrella handy for potential downpours. Even so, a very useful and information-dense app.
Currently on phone - used frequently:
Now Playing (free) - Originally called 'Box Office', but apparently that name is being used by someone with deeper pockets. The guys at AP could learn something about iPhone development from Cyrus, the developer of this app. New features are added, but they're generally either useful (ratings of movies taken from Rotten Tomatoes or Metacritic, links to trailers, links to movies and showtimes based on proximity to your current location or default location, ability to 'favorite' a movie for quick access to info on it) or can be turned off if desired (upcoming movie and DVD releases). I don't go to a lot of movies in the theater, but it's not an exaggeration to say that since I got Now Playing, I haven't seen a movie without checking it in this app first. I think that's pretty high praise for a free iPhone app.
Currently on phone - used multiple times per day
Facebook (free) - I don't need Facebook; I suspect most of us don't. But it's odd the way it helps me stay in at least nominal contact with folks I otherwise would go months or years without hearing from or about. It lets me keep up to date with major events in my friends' lives, and even lets me plan some events days before they happen. And it gives me the chance to try new things in the guise of trying to reconnect with old friends -- I went to a new-age health and wellness expo last weekend based on the Facebook invite of a woman I had a crush on in junior high. I'm not sure whether it's an advantage or a drawback that the iPhone app doesn't allow access to third-party Facebook apps (save in the sense that apps that put notifications on your Wall will show up in the app's notifications list); my gut feeling is that I'd rather the app be a no-frills gateway to my Facebook contacts and conversations (and it still needs a few tweaks to do that seamlessly), much like I want a news reader to give me news and not videos on 'hot philologists'.
I don't need Facebook, but my life would probably be duller without it.
So most of the apps I've ever downloaded end up in a virtual dustbin; that's not too surprising, I guess, given Sturgeon's Law. (Ninety percent of everything is crap.) Still, if one out of ten iPhone apps I try become apps I use regularly and get real value from, I have to consider that to be a really good ratio.