This situation will probably not affect most iPod owners but there is a 5 account limit in place for iPod song syncs. Although iTunes seems to be able to handle songs from an unlimited number of accounts, you can sync music from up to 5 accounts to any one iPod and not more. Bad news for large families with multiple accounts, but good news for the RIAA I suppose.
Update: So Mike and I ended up in a discussion about this. My point was that it made sense to create accounts for your kids so that they were licensed to their own music and could take their music with them when they went off to college. Mike answered that people should just buy DRM-free music at Amazon or Amie Street or wherever. My question to any lawyers out there is whether it's legal to gift un-DRMed MP3s to your kids and let them "take' the music with them. Thoughts?