I really think iCloud is going to be a clusterfuck for houses that have multiple Apple users that share somethings but not others.
For example, my girlfriend and I share the same purchased applications, music, and videos. We have separate Game Center accounts. We have separate Twitter accounts. We do not share mail, calendars, contacts, reminders, bookmarks, notes, photos, or application data/documents.
So how do I set up her phone so that she shares the same iTunes/shop account but has her own separate iCloud account?
Edit: Bonus controversy; we
do want to share photos on desktop platforms, so iPhoto should be able to download photo streams from both hypothetical accounts