Mehdi is referring to users' tendency to use Google for online searches without a second thought. It's almost second nature to them. Many people even head to Google as their first webpage when they're testing to see if they have an Internet connection.
That's what Microsoft is up against, despite all the money it has invested in Bing, which launched over a year ago. Bing has gained share since then, but it is still nowhere near Google. Microsoft has been running advertising campaigns, both online and offline. Awareness is not, however, enough to break people's routine.
Google says Bing is its biggest competitor: bigger than either Facebook or Apple. Furthermore, the search giant has retaliated and significantly improved its services in the last year, including Instant results and Instant Previews. Even if you never plan on using Bing, you have to thank Microsoft for stepping up the competition in the search space, essentially making Web search better for everyone.