Video Units always seemed strange to me. Basically they would scan your pages for keywords like usual ad blocks, and display text ads as usual, but the ads would be displayed along with YouTube videos chosen based on the same keywords. So you end up with automatically chosen videos being displayed on your site, along with some ads.
I’ve always thought of video as content, not a supplement to advertising, and I like to be able to control what content goes on my site. Virtually random videos seem like an odd idea to me.
Plus, wouldn’t that mean that you (and Google or course) are making money off someone elses’ videos, while the creators don’t get any compensation? That hardly seems fair. (Warner Brothers, or some other hollywood company, certainly wouldn’t think so if their clips came up in the units now and again…)