To Microsoft's dismay, Bing's gains aren't coming at Google's expense. The search giant held on vigorously to their share, climbing since the beginning of the year and holding on to more than 65% of all Internet searches in the U.S. Bing's growth is coming largely due to Yahoo's loss, which tells us that most people who are hooked on Google are not switching.
Even if Microsoft has something going good for it with Bing, it's not yet enough to entice Google users to jump ship. Microsoft is likely now pushing for more integration and "default search provider" deals with other software companies. Google capitalized on that with things like Firefox, which definitely helped bolster their share.
Microsoft' strategy from here isn't clear. They have a lot to consider, especially if they truly want to erode Google's share. Advertising deals seem likely, though the larger issue is convincing people that Bing has something better to offer than Google.