Just got from AT&T:
Valued Customer,

This e-mail is to provide an update to a network problem that MAY affect your Mobile Service.

Trouble Ticket: TT000006216509
Severity: 1-High
Description of Issue: Degradation of RIM Blackberry services Location of Issue: All Regions ;All Markets and surrounding areas Start Time: Feb 11 2008 12:20 PM PST Symptoms you MAY experience: RIM Blackberry users may be unable to send/receive messages or may have difficulty connecting to the network.
End Time: Unknown

UPDATE: RIM BES service should be returning to normal. Messages sent during the outage will arrive withing 1.5-2 hours.