I recommend don't freak out check insideadwords.blogspot.com for updates directly from Google guys about the performance and uptime of adwords system. Or if you are lazy to follow all the postings just check this thread in webmaster world from adwords employee:
he regularly updates on system maintenance here.
AdWords system maintenance on April 18th
On Saturday, April 18th, 2009, the AdWords system will be unavailable from approximately 10 a.m. to 2 p.m. PST due to system maintenance. While you won't be able to sign in to your accounts during this time, your campaigns will continue to run as usual. We apologize for any inconvenience.