Check your Yahoo backlinks.
As of a couple days ago Yahoo started discounting many backlinks to all websites when you use the "site:www.yourwebsite.com" function.
Personally I could not be happier. To me all the site results from Yahoo were garbage. You could try to check the backlinks of a competing website in Yahoo and see maybe 100k results.
Now out of the 100k results 90k of the incoming links would be from the same damn website. All these webmasters were doing is getting site wide links from websites. This is a tactic to try and trick the search engines into believing they really had more backlinks than they actually do.
It looks like Yahoo is following in Google's foot steps in cleaning up their algorithm. Some webmasters have seen devastating effects of this in the search engine position results and others have risen to the top.
Every website that I have personally worked on for the last 4 months has risen to the top 10 if not 5 for it's main keyword phrase. I can attribute this to only building high QUALITY backlinks not quantity. The honest truth is that 95% of my backlinks come from trusted strong directories.