Google Video tries to promote captions and features a small list of videos that have captions. Although adding video captions was available in the video status section, I didn't see any video with captions until today.
It's really strange that Google supports only SubViewer (*.SUB) and SubRip (*.SRT) formats, instead of focusing on professional formats used in television, for example. Most people who upload their videos won't take the time to create subtitles, as this requires a software and it's not very easy to do.
Some speech recognition combined with an automated translation software would be really useful in this area. Or at least a collaborative captioning system, similar to the way volunteers translate Google interface.