Looks as if there might be a nationwide GMAIL outage affecting not only Gmail but also Gmail via Apps for Domains (which I use for my company). The error message returned is a “Temporary Error 502″. I have seen numerous reports via Twitter and Friendfeed of other users not being able to access Gmail. So if you can’t get in at the moment - you’re not alone - use https://mail.google.com/mail/h/ to read your emails via the html interface - unfortunately you won’t be able to reply.
Update: 8-11-08 6:20 pm EST - Gmail appears to be returning to service after an approximate one hour outage for nearly everyone.

Google Temporary Error 502 - Announcements and Alerts