There is some news on the AdSense blog.

AdSense is introducing expandable ads.
In response to a click they can grow to use more of the screen.
They can also play videos.
adsense.blogspot.com/2009/03/i ...

AdSense can also now serve third party ads.
adsense.blogspot.com/2008/05/i ...

Washington Post story:
washingtonpost.com/wp-dyn/cont ...

paidcontent.org story:
paidcontent.org/entry/419-goog ...