We've looked before here at how the web allows greater slicing and dicing of a market, along with the greater reach. One of the boom aresa is in dating, where before it was based upon ads in magazines, a high cost way of trying to reach the market. In economic terms, high transaction costs, thus an inefficient market.
The web brings these costs down dramatically, thus making the market much more efficient. There's a greater reach possible, but also more discrimination in the market, as this Black Singles site shows. Looks like it's very sucessful too, hundreds of people joining every day.
Worth checking out.