I've noticed some stability problems in this beta version whenever I attempted to change a tag on a song that either might be playing or just finished playing. I've just downloaded  so I don't know if this is an issue that has been previously reported and fixed or not.
I had a minor problem after upgrading my iOS to the current 5.1(?) that the album artwork was either missing or no longer properly linked so I deleted the songs from my iPod and resynced and everything was there. iPhone syncing with the beta versions working fine.