Microsoft get inspired by Ask and created Bing. I think they took into consideration Google search engine, So Bing will come up fast even if it's better than Yahoo
I've used google for 90% of my search if they fail me, I'll try bing until then I see no reason to change.
For me, on the newer sites, Bing is sending WAY more traffic in Google. In part I think this is because of BING's ranking algo is diff. than G's and my new sites are fulfilling Bing's criteria a lot more than Google's.
I am so used to Google but I see nothing wrong with Bing. I use them both for seperate things. I use Google for Gmail, Translator, and of course Google Search. I use Bing for Maps because their birds-eye view is soo much better than Google Maps' quality.