Word is coming in from Europe that Apple is forcing users with under eight characters and without both a number and a letter to reset their passwords today. The mandate is an invisible one and some users who don’t meet the criteria are just getting empty login failures. The fix is easy. Just head over to the MobileMe and reset your password to one with the appropriate strength.
IMAP Mail and other native applications will not have been affected.
In a possibly related note (and/or some unfortunate timing), Apple Discussion Forums are down for some. If you look at the iPhone forums for example, you’ll see no posts after about 1 AM this morning. (image below)