Firstly, I think Bing has a chance to chip away some marketshare from Google, especially since iOS uses Bing now. More users mean better results and to be honest, they're already pretty good. But, they're a few things they need to fix:
1 - Bing's reputation. Seriously, don't try to find out what "the internet" thinks of Bing. You'll only find more negativity and ridiculizations when searching for Xbox One GIFS.
2 - Innovation. I like the "one photo a day" feature and the Facebook integration and the Rewards, but Bing needs MORE stuff Google doesn't have. Seriously, they need to start pumping little gimmicks, they don't even need to be that functional, but just to help people explain why Bing is better than Google.
3 - Devotion. Seriously, Bing's still in beta here in the Netherlands and in tons of other countries. I don't get ANY of the above innovative features (well I get a photo every day, but that's that).
Let's hope the new "devices and services" approach will tackle these points.
Secondly, I don't know if Facebook is that easy to "overthrow" (not by Socl OR Google Plus). Yes, it happened before with MySpace, but that was just evolution; survival of the fittest. I think Facebook might be the most succesful kind of his species. Every "new" social network is an improvement on the previous one, I'm wondering if we've reached the limit with Facebook... It's not just a place where you post your thoughts, it's so much more than that. Events, messaging, memories, video calling... People don't easily turn away from a platform like that.