At the launch of the myTouch 3G, Google says that there are now 5,000 apps in the Android Marketplace. There’s going to be a special T-Mobile “app pack” soon that’ll tie together some T-Mobile apps along with some third-party ones that they like.
Also, for T-Mobile customers, there’s going to be a direct-to-bill payment option for apps (so it shows up on your phone bill, in other words), so buying apps will be a little simpler.