The new search feature actually searches each show’s closed caption text. Doesn’t sound like any time soon you’ll be able to search for “Robots” and get a list of all video clips where a Robot appeared. Who knows. Maybe this will be down the road.
Of course, television networks could post their transcripts (I imagine some do) and make searching easier–outside of categorizing the contents as television content.
Occasionally I’ve wondered about searching other types of non-text content–like Webcasts and Podcasts. One trick would be to work off of a transcript, but of course, most don’t have transcripts. In the Commons License part of the world, this might be doable if someone would create a transcription service for these types of content. Each content producer could publish a link to their latest content to a service that would transcribe it. Like most net stuff I imagine this service would have to be free and ad supported.