I'm adding my problem to this list in hopes of figuring out the problem... I have an added twist.
The reason my email was changed in the first place was due to fraudulent charges made on my itunes account. Apple froze everything and it created a HUUUUUGE mess. I couldn't do ANYTHING with my account for over a week while they figured out that telling me to reset my password ten different ways was NOT going to fix anything. I have, in fact, added the OLD email to my current account and verified it, but it STILL won't work. I'm sure Apple has some sort of block on the email address, but dealing with the aggravation of explaining it all to their tech team again makes me feel sick...
The free iCloud account is pretty useless anyway, so it's no big deal that I can't log in, but it is annoying.
I guess I will just wait for the "bug fix" iOS7 update.