I have a related issue. Facts;
a) My AppleID is an old mac.com address. My mac.com / mobile me account was not active, and I wasn't using them email address.
b) I can't change my old mac.com apple ID
c) I downloaded ios5 to my ipad2 and my wife's ipad1.
d) My wife's ipad1, using that appleID, works. Icloud is backing up things just fine.
e) On my ipad2, if I skinny down the back-up to really small (<5MB), it appears to work
f) However, I need to buy more memory. When I do that, I first get a "your (presumably AppleID) email address has changed, click to continue" after entering my password associated with the mac.com ID.
g) After I re-enter my password to continue, it hangs forever in the "buy memory" dialogue box.
I think this may be related to my issue of having an old mac.com address as my AppleID. I have updated my AppleID password to a conforming one (at least one capital, #'s, etc.), but still the same issue.
Thoughts?