I've had the Palm Pre for about 10 days now. I like it a lot! The slideout keyboard is nice, and while some people consider it to be a bulky phone, those people are crazy. It's certainly smaller than my Treo 600. The form factor isn't for everyone (as
jessnut noted) but it works fine for me.
The App Store is kind of poor right now, but that's largely because they're only allowing free apps on the store. That *should* change tomorrow with the new OS and App Store update, although it looks like it might get delayed until next Thursday. The games that are currently available are mostly competitive classic board games (like Reversi and Chess) that are very easy due to poor AI. For some unfathomable reason, there is no Freecell implementation available. You don't even have to program an AI for Freecell! Come on, people!
There's also a pretty strong homebrew scene but I haven't gone through the motions needed to get homebrew apps on my Pre yet.
One app that I have been getting a lot of mileage out of is the Pandora Radio app. I'm also going to experiment with using the Pre as an mp3 player -- I can't fit all my music on there but I might just keep a few of my most recently purchased albums on there, essentially like having my 6 CD car changer with me at all times. It won't replace the iPod on long trips, but for riding the subway (where I don't get Pandora access), it might do the trick.
As far as its functionality as a phone, it's okay. I haven't hung up on someone by accident yet, and it's easy to get to your recent call list. One problem is I don't see a speed dial functionality. The contacts list is fantastic -- it synced my old Treo contacts list with my Gmail and Facebook contacts as well. It did this entirely over the air (well, minus the Treo part). And it's smart enough to know that Nicholas Smith at 555-123-4567 on my Treo is the same as Nick Smith at 555-123-4567 on Facebook, and it merges those contacts invisibly and automatically. I will say that it's weird that I now might have a lot of people's phone numbers that I didn't know, if they include their phone number on their Facebook profile. When I was at GDC Austin last week, I said, "Well, I'll search my phone for this guy, it may know his number." Lo and behold, it did!
Web browsing is perfect.
My main problem is one that I'd have with an iPhone anyway: the OS can do so much more than PalmOS, but PalmOS was just plain fast. I would press the shortcut to go to my ToDo list and it would instantly load. Even with a shortcut to my ToDo list on the Pre, it does take a perceptible 0.5 seconds to load up the app. I miss the immediacy of PalmOS, where it was almost like writing on paper: it just worked, no load times for anything.