Just noticed this:

“System downtime – 18 March 2010 10:00 to 18 March 2010 14:00 Pacific Time.

AdWords system maintenance is scheduled from 18 March 2010, 10:00 to 18 March 2010, 14:00 Pacific Time. During this time, you won’t be able to sign in to your account, but your campaigns will continue to run normally. We apologise for any inconvenience.”

Four hours? During the middle of a weekday?