Google adsense ads have always been pretty drab. They're basically a small rectangle with some text and a link to the advertiser's Web site. Here's Google's attempt to make adsense a little more interesting by applying a little holiday style.
I can't say if the holiday spirit background has made them more prominent to generate more clicks, but anything besides the old boring format is a welcome change. At least it makes them look a little livelier, especially on sites like mine that look pretty boring to begin with.