A WebmasterWorld thread reports Google AdSense going down at about 1pm (EST) and finally coming back up at 3pm (EST).
What concerned many publishers was the fact that there was no warning from AdSenseAdvisor in the forums. There was however warnings from AdWordsAdvisor that the AdWords console and API will be inaccessible during that time.
A Google Groups thread has a post from the AdWords rep:
We'll be performing routine system maintenance on Saturday, March 8 from approximately 10:00am to 2:00pm PST. You won't be able to access AdWords or the API during this time frame, but your ads will continue to run as normal.
Cheers, -Jeffrey Posnick, AdWords API Team
However, the last AdSense announcement was posted in Google Groups back on January 11th with a heads up about maintenance to take place on Saturday, Jan 12, starting at 10am PT.
Forum members at WebmasterWorld are getting a bit concerned that AdSenseAdvisor's last post was on January 11, 2008. They are concerned the representative is either sick or no longer devoted to the forums.
Forum discussion at WebmasterWorld.