Over the weekend, many AdSense sites, were not serving up paid contextual ads. Instead, they were serving up what are called PSAs or Public Service Ads. They kind of look like this:
They do not earn publishers money.
A Google AdSense Help thread has confirmation from Google on this bug. AdSensePro Ashley said:
This issue has now been resolved. PSA ads on affected blogs should now be replaced with paying ads. Some publishers may experience a short delay before they see paying ads on their blogs.
It might have impacted just Blogger/Blogspot blogs. But it impacted many blogs for a short period of time. There were 45 responses to this small "crises." There was also discussion at DigitalPoint Forums.