As we predicted here, the big Bing event had to do with Facebook data being used in searches. Effective immediately, when you search on Bing you can see results based on what your friends and other people are recommending and talking about. So your search results will be different from mine because we know different people. (unless this is me re-reading this blog post in which case, hi John).
It's the largest roll out of social search I've seen yet. It's a pretty big win for Bing, which lets itself be differentiated from Google. And it's a fine move for Facebook in that it has nothing to lose, it can incorporate the same information on Google or Yahoo or it's own self-built search engine if it ever really wants to.