The bigger issue here (so it seems) is people like myself who have had an AppleID for quite some time, then signed up for MobileMe.
If iOS 5 has you sign in with your AppleID to keep track of music/app purchases, etc... but you have a different account for your email/contacts/calendars through MobileMe... there doesn't seem to be a decent way (at this point, at least) to merge the two accounts.
for reference, here's some people explaining the issue better:
https://discussions.apple.com/message/15351517
One of the posts in that thread contains a link to this useful document:
http://docs.google.com/viewer?url=h...351u/copying_data_from_mobileme_to_icloud.pdf
In a nutshell, you switch off MobileMe syncing for Calendars, Mail and Contacts, but when promoted choose 'Keep on my iPhone'.
This process kills MobileMe syncing, but keeps a local copy of all this data on the device.
Then you switch on iCloud, and the data is migrated.