Google is previewing Google Video, which allows you to "search the closed captioning text of all the programs in our archive for relevant results ...[and] look through short snippets of the text along with still images from the show." There are more details at the About Google Video page...

Google has also raised the word limit in its search boxes to 32 (from 10), allowing for more complex and customized searches.

Update: I should have mentioned that Yahoo also released its own video search a couple of weeks ago. I haven't thorougly tested either one yet, so YMMV.