I installed the 2.0 update and downloaded and played with a bunch of the apps. Except for Enigmo, all the apps I tried were free. The high points are Cube Runner, Aurora Feint, Shazam, and Google Mobile App. Here's my quick impressions:
I tried several of the free ones, and based on experience with the Desktop game, I bought Enigmo. The iPhone definitely has potential as a gaming platform.
Cube Runner: This is a nice little game that uses the accelerometer. The control is nicely sensitive and the game is cute, but it gets sort of old quickly, but it's fun enough to do in an idle minute I'm unlikely to delete it.
Aurora Feint: This has some role-playing game back-story, which I haven't really figured out, but it's a great little Tetris like game. You've got blocks of the 4 elements and you're trying to get them in rows of 3 or more, in which case they disappear. It's got good use of the touch screen, and you can even rotate the phone to switch gravity, which is a nice (literal) twist on the game. Good graphics, good play, good sound, and who knows, the bigger game might be interesting too.
Enigmo: I enjoyed the desktop version of this and the iPhone version is a remarkble port. The controls are sometimes a little finnicky, but it works and the puzzles are great.
PhoneSaber: Makes your phone make lightsaber noises as you swing it around. Gratuitous fun demonstration of the accelerometer. Don't let go.
Blip Solitaire: A pretty basic game that uses the touch screen. Not really any fun. Haven't deleted it yet, but probably will.
Spinner: Another acelerometer based game, but just not that compelling. Not intuitive and once you figure it out, not that fun. I'll play Cube Runner instead.
Shazam & Midomi: These are two "music id" services. Both let you hold the iPhone up to playing music and it will try to identify the song. Shazam seems to work better for music over the radio and has a reasonably nice interface, including of course "Buy from iTunes" buttons, but also has "Watch on YouTube" buttons. Very nice for IDing a song on the radio in the car. Midomi is also pretty good, but it's key feature is that it lets you sing or hum a song, instead of just actual music. It does pretty well, and my kids got a kick out of singing Twinkle Twinkle Little Star and having it recognize it.
Remote: A very nice and remarkably responsive interface to control iTunes on your desktop. It makes me want to get an AirPort Express.
Jott: Transcribes little voice recordings. It's not as featureful as the full Jott service, which I hope they will fix. The transcription latency is also really high, and while you can get your notes emailed to you, it's on a daily basis, not ASAP. If this improves, it will be great. For now, it's more of a net (slow) trick.
VoiceNotes: A basic voice recorder. The interface is a little clunky for most of the circumstances I've used a voice recorder in the past.
Google Mobile App: This is QuickSilver for your iPhone. If you haven't used QuickSilver, it's a cool mac app that doesn't do anything new, but does a lot of old things better. The Google Mobile App doesn't really do anything you can't do in Safari, but it's better at doing them than Safari. Basically, it saves a lot of typing by doing search term completion, web site URL completion and background searching. The web site URL completion alone is worth it to me, since the iPhone's (otherwise excellent) keyboard spelling correction doesn't do so well with URLs.
Twitteriffic: I'm not really big into Twitter, but this seems like a decent/nice interface to reading and posting. That said, I hear people raving about how great this is, and I don't quite get it. It's good, and includes nice things like easy posting of pictures, but really, I don't see the excitement.
LifeCast: I haven't really tried this one out much, but it seems like a nice interface to mobile blogging (Blogger or Tumblr). It doesn't seem to know about the fact that Blogger supports multiple blogs per user so I haven't tried it yet.
Yelp: I was hoping this would be great, since I really like the web site, but it couldn't find any restaurants near my home, which is just wrong.
WeatherBug: A decent weather app, but rather than showing cached results and indicating it somehow while it loads the updated information, it blanks out the information, which is annoying, especially when looking for forecasts which don't change that often.
eReader: A book reading application that comes with a couple of free books. A decent first pass, but it's missing a lot of features I'd want like bookmarking, line spacing adjustment and such. Plus, the page flipping UI gets the z-order wrong when going backward, which is a little bit dissonant.
NYTimes: Not bad, but nothing special as an alternative to the web site to read the news.