The good news is that objective third party observers consider Microsoft's Bing as good a search engine as Google's. The bad news is that most current users will stick with Google out of habit. The real news is that it doesn't much matter at this point, because Microsoft is in it for the long term.
Search engines, and similar applications, are in their infancy. They were invented by member of our (Baby Boom) generation for the use of the following two generations, X, and Y. It's true that Google has gotten a large share of early users (Boomers). But most of this group have either adopted/adapted to this application, or are unlikely to do so.
It is the following generations whose members have yet to make their choices. And here, MSFT is at no disadvantage relative to GOOG and probably at an advantage. The following two generations (unlike Boomers and their predescessors) will have to deal with many other computerized office applications, some of which Microsoft excels at. Put another way, Google is a one-product company; Microsoft is a multi-product company, which is to say that there are many ways for it to bundle Bing with other applications in the not so distant future.
MSFT's share (not counting Bing) is at 8% and rising.Yahoo's share is at 20%, and falling. Google does have the lion's share, about two-thirds of a relatively small market. Given the two companies' relative "scalability," it seems that MSFT's share will rise,and Google's will fall, as the market expands. Yahoo, on the other hand, is the odd company out.
Disclosure: Long Microsoft.