Podzinger will deliver you an RSS feed of any search result -- you can bake in a search for your favorite keywords and get an alert -- with timecode! -- every time the keywords show up in a cast.
This is all de-militarized technology from DARPA's EARS (Effective Affordable Reusable Speech-to-text) program, and it's been developed by the venerable BBN company, which was also part of the initial development of the Internet.
Podzinger only works in English right now, but they're rolling out "North American" Spanish and Mandarin shortly.
The only downside is that Podzinger doesn't run well on Firefox for the Mac, because of known bugs with the way that Quicktime and Firefox play together. Mac users have to switch back to Safari to use it. Still, it's a small price to pay for a killer free service.
Update: Dave sez, "Our product, Podscope, is like Podzinger, except that we also index video blogs and have a Firefox-friendly design."