I know all people has the same question: why Microsoft chose Bing as their new search engine site domain name ?
Actually all the people who has relationship with Microsoft might have already given the answer.
But I have different thought: I guess Microsoft wanted to name their new site "Bingo" at the beginning time. Because normally people got the right result or something which they wanted, they can say "Bingo !", However, "Bingo" has the similar "tail" sound like "Google", Then if Microsoft use "Bingo", people will think they followed "Google".
And, the domain name "Bingo" must be more expensive than "Bing".
So Microsoft chose Bing finally.
Just my own guesses.
For other opinions, please read here or search from internet.