Today Google launched Youtube Video Units that partners can integrate into their sites. See a working example Youtube video unit below.

The customizable video player offers videos relevant to the site. There are companion and text overlay ads that generate revenue for the Adsense partner.
There are only 3 sizes of the video player to choose from. The smallest is 400px wide. The other two are even larger.

I am not sure which sites have that kind of real estate available to integrate video units. I have not yet seen what kind of videos Google will show in the viewer below. I am as curious as you.
Via Google Adsense blog.