For those who have two Apple ID's, we have to wait until the official release. In the interim, this is what I have done:
1) I have a Apple ID attached to iTunes that has all of my purchases on it. That is the one I used for iCloud.
2) I have a MobileMe account that has my @me.com e-mail address. It also has my contacts and calendars.
3) There is currently no way to migrate your @me.com e-mail address to your iCloud account. You have the option of creating a NEW @me.com address for your iCloud account, but I have chosen to leave Mail off for iCloud. If you create a new one now, I'm not sure you'll be able to migrate your old one over? So for now, I leave my MobileMe on under Mail settings.
4) Contacts and calendars are in a similar situation, though you CAN migrate them to iCloud now. However, I would not recommend it because I ended up with duplicate contacts in the iCloud and there's really no easy way to manage it yet. So I've left mail, contacts, and calendars turned on for MobileMe.
5) There was a leaked PDF explaining how to sync your contacts/calendars to iCloud from MobileMe. You basically sign in with MobileMe and changed your sync range to "all events" so it has everything on your device. Then you turn off Calendars and Contacts in the MobileMe settings and it will ask you if you want to keep the data on your device. You should answer yes. Then you turn on Calendars and Contacts ON under iCloud and it should sync them all over to iCloud. However, now your MobileMe won't be modified when you make changes, and it ended up causes the duplicates as I mentioned. So I just went back to MobileMe and turned the iCloud calendars and contacts back off again.
Hopefully there's a better/easier solution once we get closer to release!
