It's been in the works for quite some time and now Google's speech recognition for video is ready for limited release. For now it's only available with select political videos, but that will soon change. Simply enter in the word(s) you want to find in a video and you will get a list of videos that include that word or term, and small yellow dots on the play bar indicating where in the video it can be heard.

You can test it out here, and also add it as a widget in your iGoogle page.