According to MobileMe System Status, Mac Preferences, Windows Control Panel, iChat, and the www.me.com WebApps are down for the count. (Just how hard did they hit the eggnog over the last few days?)
Still, they're keeping some pretense of holiday spirit, or irony:
All other MobileMe services are online and fully operational
Let us know how badly you're affected, and when things start going smoothly for you again.