These three search engines have the vast majority of all searches done in the U.S., over 90%.

(Bing is the search engine formerly known as Live, and before that, MSN. Microsoft's search engine.)

Google is around 2/3 of all searches, Yahoo around 15%, Bing a few percent.

Here's the results of an actual "blind test" (meaning which search engine they were actually using was hidden from them):

Google vs Bing vs Yahoor.

Google wins, though not decisively. Bing and Yahoo almost tie (so much for what a new and better thing is Bing).