I used to work in a record shop and one thing that happened quite often was a customer coming into the store asking for help finding a particular song. Often, the customer didn't know the artist or title but could sing some of the lyrics. That was years ago, back when I had hair on my head. Jump to today and news from multimedia engine GoFish that they've just launched a new advanced search feature (beta) that allows the searcher to search by song lyrics.
Granted the database is currently small but it's growing daily. I had good (not great) results when searching lyrics for popular songs from the 60's, 70's, 80's, and 90's. The option to search by lyrics and then simply click and purchase the track/CD is a great value added search option that I would bet we'll see from other online music and multimedia search verticals in the future. Kudos to GoFish for getting the ball rolling!