Don't use Betas #1: iTunes Music shopping and OTA sync
I am legally testing the upcoming iOS 5 on my iPad 2 and was quite happy to try the Music application with the new Beta 2. So happy that I thought "ok, you buy your next music now directly on the iPad and see if it syncs over the air back to iTunes".
Well, I failed and needed to request a re-download from the support as you can see from the screenshot.