That's a form of fallacious reasoning called an Argumentum Ad Populum, or an Appeal to the People. That something is generally believed does not prove that it's actually true. Popular opinion is quite simply irrelevant (non sequitur) to the conclusion. For example, at one time pretty much everyone thought the earth was flat... popular belief didn't prove the statement.
Hence, "Everyone says that Google is better than Bing. Therefore, Google is better than Bing." Is just fallacious reasoning.
On the other hand, it doesn't mean that what's popularly believed is false. It's just that the truth of a statement cannot be determined by appealing to popular opinion (Unless, of course, the statement is <I>about</I> popular opinion. LOL)