Traveling through dozens of sites with AdSense ads on them, you'll notice ads that look like the one directily below.
These are called "PSA"s, or public server ads and are served up in place of Google AdSense contextual ads when Google has no more ads to serve up. This normally occurs towards the end of the month when AdWords customers run out of funds in their accounts. But this seems to be a little different, because it seems some very competitive keywords - where budgets do not 'run out' - are serving up these PSAs.
There is forum discussion about this level of PSAs being served up. Speculation is that the main Google AdSense server is having technical difficulty and PSAs are taking its place temporarily. We will see how it folds out.
Forum coverage at:
Oh, I just added alternative ads to this site so I won't server up those PSAs.