The interesting part of all this is that Bing was created not because Microsoft wanted to be in the search business - but because search was lucrative enough for Google to allow them to grow into a threat to Microsoft's core OS and Office monopolies. Bing is there to cut Google down to size more than to build up Microsoft. And, to the extent that Google actually had ambitions to take Microsoft head on, I guess they were right. Though who knows - if Microsoft hand never tried to damage Google's revenue stream, maybe Google never would've gone after Windows and Office. But the Google guys were nothing if not ambitious.
You could also make the point that Android was more an attempt to keep Microsoft from buying their way into mobile search than any kind of attempt to take on Apple. But all these companies counting on network effects to maintain near monopolies seem to have to take on all comers. Monopoly power, for all the head start it gives you, are not invincible.
No... just, no... Google has never been a threat to Microsoft's OS. Their mobile division, definitely, but never their OS division. As far as Office goes, they have been a minor pest, at best, with their email service. Google did win the search war and they have had huge success with mobile, but have had a hard time turning Android into anything resembling the financial returns that Apple is getting from their mobile business.
As for any comparison between Facebook and Bing, it falls down on it's lack of merit alone. Bing has never been popular, nor has it had critical mass. Facebook has a critical mass that will be very difficult to overcome. When your grandmother, mother, cousins, uncles, friends, etc. are all on the same service people aren't about to jump ship.
Snapchat may be popular with teens for inter-personal sharing, but they still use Facebook to communicate with a wider audience. That's why Facebook is mimicking their capabilities. It's also likely why it won't work. Teens have always sought out their own way of communicating with peers, whether it is language or a separate app. But as they get older, they will and do use Facebook for the simple reason that Grandma isn't using Sanpchat, but she is on Facebook...