Those folks are terrible clickers.
Has your percentages of traffic from each source type changed recently?
I would bump the maximum number of ads per post from 1 to 2.
I would also try using a background color for the ads that matches the background color in your content. I would also try that on the 160x600 wide skyscraper ad in your sidebar.
I would also try changing the URL color to #000000.
As per usual, you will have to measure the results of each change on your site.
Also, I just linked to you from My Basketball Layouts.