The App Catalog is where the Pre 'plans' to offer the apps to add on to the phone. I say 'plans' because right now, the App Catalog is in Beta. There aren't many apps in the app catalog, and what's there hasn't wowed me. There may be some useful apps that I haven't tried there, but they're likely in an area that isn't of great concern to me (like stock watching). I have downloaded Accuweather, which is nice and polished, Pandora, AP & New York times feeds (which I rarely look at, but appear to present news), Sodoku, which is fairly standard sodoku, and Splash ID, for storing personal information. Looks useful. Beyond that, there isn't much in the way of applications.
As I indicated in an earlier post, there is no Facebook or similar app (just LinkedIN). There are some other social networking tools, but nothing that really grabbed me. There is only one game, a demo of Connect 4, which I didn't bother trying since I understand it is limited in use on account of being a Demo.
I'm hopeful that with Palm's SDK out of beta now, apps will start showing up, but I'm not holding my breath. They've got a long way to go to catch up to iPhone;s and Google's apps. The positive note about that though, as a friend pointed out, I don't have to worry about sifting through hundreds of useless apps to find a good one, as you need to do on the iPhone or G1. I might be willing to trade that in though to be able to have some handy or fun apps on my Pre