I couldn’t register using the username I had used during a .Mac trial that expired a few months ago.
The MobileMe account support form kept refusing submission, saying “Please enter a valid email address”, regardless of the many valid email addresses I tried entering there. I eventually gave in and picked a different username.
The password I initially selected never let me successfully log in, even after I “reset” it twice to the same thing. It only worked after I changed it to something else.
I keep wanting to investigate the “Upgrade storage” options, but clicking all over the account-upgrade banner in the web account-setup page does absolutely nothing.
The first time I tried syncing my home computer, the System Preferences panel kept unchecking the synchronization box until I signed out, then signed back in. This didn’t happen on my laptop.
At least now, it seems to be working.