Some of the Google AdSense ads have recently been served and tracked via DoubleClick. Here is a picture of me with my mouse over a Google AdSense ad from my personal blog. As you can see, the tracking URL is http://googleads.g.doubleclick.net/pagead/iclk?.
I am not the only one seeing this. A few publishers are noticing this and commenting on this at WebmasterWorld. Some suspect it has to do with the poor earnings people noticed over the weekend, which we will be writing about within the next hour or so.
Forum discussion at WebmasterWorld.