I was just using Last.fm tonight and noticed what appears to be a new Adsense ad unit (screenshot above.) Besides looking completely different, there was a underline style mouseover.

This is very interesting. Its clear to me that as people start to place “Adsense” into the catagory of advertising they kind of filter it out and don’t read the ads. I’d be interested in seeing what effect mouseover link has on clickthrough rates (besides the new style,)

(update: Jen from Jensense Contextual Advertising Blog says this is a “custom ad unit that premiums and select regulars get”)