Google is pretty much the main search engine, but Yahoo and Bing also count for something. If you've got a Google Analytics account you'll notice right away that not all your traffic is coming from Google. I get quite a bit from Yahoo, and even some from Bing. I've got a guy I work with (new guy) and I found out that exclusively uses Bing as his search engine (he's not a marketer, he just uses it for browsing the internet). I didn't know such people exist. He's kind of a hipster type, so it makes sense, but the point is that even Bing counts for something.