Google will be testing Adsense video distribution. They did something similar last year with MTV however there are some big players involved this time, warner, Sony and others. Check it out : http://adsense.blogspot.com/2007/01/this-is-test-video-content-on-adsense.html
Yeah, got an email about this today. It might prove to be pretty lucrative, especially with a couple of music-related sites I have. They have some major music advertisers available that will be providing fresh content on a daily basis. Basically, an additional source of content without having to do anything. For those who are wondering, this won't count as one of the 3 ad banners you are limited to.
As mentioned, it's fresh video content delivered to your site daily by the advertiser, who recycles it whenever they have something new. It also doesn't count as one of your three allotted ad banners. If you have a specific niche that there exists narrowly focused ads for, you can make some nice change by offering new content for that audience every other day/week, etc. It's also not contextual as far as I know, as it is advertiser-driven.