To try and compete with the likes of Google, Yahoo are updating their advertising system to allow advertisers to target users according to the query they type into the search box.
This is all very good for advertisers, but Yahoo also need to try and increase the number of people who use their search engine. I, like many other people, use Google daily to do my searching, although I do have a Yahoo mail account that I use occasionally and read quite a lot of the Yahoo News pages. What Yahoo need to do now from a marketing perspective is to get more people to try Yahoo Search, and have them find that it works better than Google. At the moment, I don't think it does, personally.
Yahoo currently own 27% of the web search market, behind leaders Google with 42%.