And a major source of ad revenue comes from targeting ads to search results. It's the search and indexing component they've done rather well. It's also the first thing they did. I've been using it since I believe a month after it went live.

But even in this respect I think they haven't innovated enough to provide settings allowing users to refine or better filter their results. It doesn't help when millions of people are out there trying to game their ranking system.