From Apple's Website-
We apologize for this service interruption and are working hard to resolve the problem.
For more information, please refer to System Status on the MobileMe Support Page.
System Status
1% of MobileMe members cannot access MobileMe Mail. Service will be restored ASAP. We apologize for this service interruption and are working hard to resolve the problem.
Important: if you are affected by this email outage please click here for more information.
MobileMe: Important information regarding email service interruption
Symptoms
Updated: July 22, 2008, 4 p.m. PDT.
On Friday, July 18, 2008 (2008-07-18) we experienced a serious issue with one of our MobileMe mail servers. This issue is currently affecting approximately 1% of MobileMe members. Affected members are unable to send or receive email at www.me.com or access email using any email client software such as Mail on a Mac or Microsoft Outlook on a PC.
Products Affected
MobileMe Mail
Resolution
We understand this is a serious issue and apologize for this service interruption. We are working hard to restore your service.
This document will be updated as more information becomes available.
Wow, Apple, thanks a lot. I've been without my mac.com email for a week now.