This is hilarious: http://googleblog.blogspot.com/2011/02/microsofts-bing-uses-google-search.html TL;DR version: Google inserted bogus results for ridiculous search phrases. Amazingly, those bogus results suddently popped up on Bing. Example:
You could easily determine if your browser or any other program (toolbar, search bar on your task bar, etc.) is sending info to Microsoft's servers with your Network tools.