See it work at: http://www.bing.com/twitter.

 [UPDATE 10/22/2009]:

Reactions:

http://googleblog.blogspot.com/2009/10/rt-google-tweets-and-updates-and-search.html
http://www.businessinsider.com/henry-blodget-well-what-do-you-know-google-is-actually-nervous-about-microsoft-bing-2009-10