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.

So, what happened? I bought two albums from the iTunes store and they started downloading to the iPad just like normal. Three songs actually can't be downloaded for unknown reason. The rest landed in the Purchased playlist in the Music app as expected. Ok, let's start syncing! But oh, no new music on my Mac after that.  I quickly noticed that I had not activated to sync the Purchased playlist in the settings. Right after deleting a few gigabytes from that existing playlist on iTunes (a lot more than my iPad could handle) I restarted syncing. Again, nothing new. Last try was to sync via old-style/PC-era USB cable. No luck. I had no chance getting the new Music from the iPad over to iTunes on the Mac. Luckily the files got not deleted while syncing. Instead a lot of ghost playlists with the same name Purchased appeared in addition to the first one (one for each sync try I guess).

Now the only way for me to get the music in a save place was to request a re-download from the iTunes support team. I never had to do this before so let's see how they react and what they want me to do next :-)

Conclusion: Beta software is beta. For a reason. (be assured I know that for myself :-p)

Addition: In the meantime Apple just allowed me to re-download all songs. That was quite fast ^_^