Adwords:
"We will be performing routine AdWords system maintenance from 10 a.m. to 4 p.m. PDT on Saturday, July 29, 2006. While all AdWords advertisements will continue to run as normal, you may not be able to perform any API operations during this maintenance period.

We apologize for any inconvenience."

AdSense:
"This Saturday (7/29), we’ll be performing routine system maintenance at 10 am PDT. Although you won’t be able to access your account for approximately 6 hours, ads will still be served to your pages, and your account stats and earnings will continue to be recorded.

Thanks for your patience – have a great weekend!"

Makes me think something big is happening.

Nothing big, just the usual maintenance.