Google gathers lots of user data on 3rd party websites via services such as (to name a few):
- Google analytics (opted in for data sharing)
- Chrome
- Google toolbar
@Matt Cutts - I'd love it if you could confirm exactly which user data you DO and DO NOT use to influence rankings. Or, at the very least say on record that you don't do what Bing are doing and use data from bing.com
Overall, I'm not surprised that Bing are doing this for some keywords - all the major search engines use a massive number of different signals. I'll be more surprised if it turns out this is happening at a large scale or for competitive terms.
@Matt Cutts - I'd love it if you could confirm exactly which user data you DO and DO NOT use to influence rankings. Or, at the very least say on record that you don't do what Bing are doing and use data from bing.com
Overall, I'm not surprised that Bing are doing this for some keywords - all the major search engines use a massive number of different signals. I'll be more surprised if it turns out this is happening at a large scale or for competitive terms.