According to Henry Blodget on SAI, Bing is
Doomed to Fail
The reason almost 70% of folks use Google is that most folks like Google and most folks are used to Google. If there's a "better" search engine out there, most people probably don't know that it's better (because it's really hard to tell--in part because "better" is in the eye of the beholder), and many people who can tell probably don't care.
I recall similar said for Netscape, IE could never win.....lets see what happens when Bing is packaged as the default search in every WinTel machine.