Is Google experimenting with new ad formats?

One of our websites, www.voodoochilli.net, I have noticed that sometimes the Google Adsense adverts change to a new format I haven’t seen before. This seems quite random and there doesn’t appear to be any pattern or relation to the content of the site affecting the ad format.

Compare the following two images. The first one is the average sort of ad we get, and the second one is the new type. It’s bigger and bolder and I think it could be quite effective.

I have had to shrink the images of the ads down a bit so they fit on this blog properly, but you get the idea. I should also point out these are the 480×60 ads.