Already users can start downloading their programs (which are downloaded to their /Users/[user]/Music/iTunes/Mobile Applications/ directory as .ipa files), but you can't do anything with them until you get the 2.0 firmware (or an iPhone 3G).
So far everything is really smooth and easy to use, although it's easy to tell that the enormous amount of applications that will be available in the coming months (and years) will become a difficult thing to trudge through. It's a high-class problem for Apple, but hopefully it won't be too overwhelming to find something good if you don't know exactly what you're looking for.
We'll be keeping tally of some of the more noteworthy launch apps, although many we've already seen, and we're updating as we go. Take a look at a few after the break!