Apple announced the release Wednesday of OS 3.1, which will be a free update to both iPhone and iPod Touch owners.
With 3.1, users on both platforms can now get Genius recommendations for applications they've purchased. These show up in the App Store app, as well as in iTunes, and function in a similar fashion to Genius for music. It takes your purchase information and sends it to Apple, which will analyze it for similar purchases, and offer up recommendations. This may end up being a more precise system since there are fewer apps than music tracks.