A note on the MobileMe support page states:
MobileMe members will be unable to access MobileMe applications at me.com. Access to MobileMe will still be available on desktop applications, iPhone, iPad, and iPod touch. Normal service is expected to be restored at the end of the maintenance window.
It's likely this work will support iPhone 4 which hits the streets next week. Hopefully Apple learned a lesson from the 2008 debacle when Apple brought out the iPhone 3G at the same time it launched the .Mac re-branding that became MobileMe.