If you’re like me and share an iTunes account with my wife, but also have me.com addresses for both your phones contacts etc I have finally found a definitive answer on setting up iOS 5.

http://support.apple.com/kb/HT4895

Essentially go to settings > iCloud and use your me.com username (After converting it), and for iTunes you go to Settings > Store and used your iTunes ID there.  Same for Mac.  Settings Me.com use your iCloud info, and in iTunes use your iTunesID for your iTunes.

So you keep your iCloud individuality, but your iTunes are kept separate so they can still be shared with the family.