A week ago, Google had a bug with the AdSense contextual targeting engine which generated PSAs for all ads for a five minute period. PSAs, again, are public service ads that are shown when no ad match is found - so Google shows a free ad for a non-profit organization.
This time, the issue seemed to be at least four hours, but maybe longer. First reports came in sometime last night, probably late last night. The earliest time stamped complaint I saw about this was at DigitalPoint Forums at 12:20 this morning. Things began targeting properly again at about 4:30 this morning.
Google has yet to confirm the issue but clearly there was some wide spread issue with this contextual targeting.
Update: Google posted a blog post with the confirmation of the issue, they said:
An ad serving issue yesterday, August 31st, from 4:30pm PDT to September 1st, 2am PDT caused less relevant ads or public service announcements (PSAs) to appear on some publisher pages. This was mostly limited to regions of Asia. Our engineers have now resolved the issue, and ad targeting has returned to normal. We apologize for the inconvenience, and are working to make sure that this doesn't happen again.