If you are doing pay per click campaigns then you just might want to take note of this article. This shows the trends among the top search engines (Google, Yahoo and Bing).
What I find very interesting is the fact that Yahoo has consistently grown as Google the powerhouse has been on the downfall. Back in the day when doing pay per click campaigns most would not even consider Yahoo, Well things are changing.
Take a look at the great charts provided and really take in what they are showing. If you are doing or even considering doing a Pay Per Click campaign this will give you some great information. Also note the click through rate on the different search engines. I think you just might be a bit surprised as I was.