You never met a meta-game like this. Google Image Labeler pairs you with a random online partner and an equally random image, and you fire off as many descriptive keywords as possible in two minutes. If any of your words matches your partner's words, you are both awarded points. The game is surprisingly fun and challenging...and if you're as viciously dull as some of us are, your head may ache.
The upshot for Google (and everybody else, supposedly) is an improved Image Search function. Well, it beats not paying interns to do it.
In an effort to conform to popular pressure from commenters, here's a link to Google Image Labeler.