I have an AppleID that dates back from mac.com days, so it's say, myName@mac.com
I then transitioned through to MobilMe and so have a myName@me.com address. Now it's iCloud's turn.
When I go to set up my newly transitioned iCloud account, I enter myName@me.com as my AppleID - everything goes fine, except that my AppleID and from email address gets changed to myName@mac.com. I cannot send email at all from my iOS 5 devices using myName@me.com. It won't even present it as a choice in my 'from' field - although I can pick other aliases I have created.