This could be huge. The switching cost on search engines use is minuscule...all it really takes is for users to get acquainted with a search engine they prefer. Facebook could very well be the way a critical mass gets introduced to Bing, and if users prefer it to Google, it could be game over. Five years from now, MBAs might be reading a case study on how hubris brought down the world's biggest Internet company. Walk around the beach kicking sand in everyone's face, and eventually, someone (or some group) will take you down.