Yahoo is actually the most visited website in the world because it is a content site but it currently only controls about 20% of the search market. It would make sense to combine with Microsoft and MSN which is going to be the only way they will be able to compete with Google moving forward in my opinion. Here are the most recent Comscore stats on Yahoo’s percentage of the search market:
ComScore: Yahoo! Web Search Reported Total Search Share (US)
They really have not grown their share and with more competitors hitting the market and Google growing their monster engine, it will be tough for Yahoo moving forward. This being said, our clients at Internet Marketing Inc still get decent results and high conversions from Yahoo. In fact sometimes conversion rates are actually even higher on Yahoo than they are in Google. With the recent CEO change, I am excited to see how Yahoo grows moving forward. I actually still use them as my home page and personal search page over Google but apparently I only make up 20% of people. Check with your internet marketing company to see what search engine is right for you and your business. Odds are that it will be a combination of all the major search engines.