1. If you have opted in for IE8 Suggested Sites or installed Bing toolbar,
“When Suggested Sites is turned on, the addresses of websites you visit are sent to Microsoft, together with standard computer information. "
"To help protect your privacy, the information is encrypted when sent to Microsoft. Information associated with the web address, such as search terms or data you entered in forms might be included.”
This means Bing can get your Google queries and Google search results.
2. Google now claims that Bing has been using this and copying its results and using it in as a ranking signal in its own search results.
Google manually ranked sites for 100 different gibberish search terms that had no results in Bing or Google. 20 engineers then installed the Bing toolbar and performed searches for those gibberish terms using Internet Explorer, clicking on the page they'd previously manually ranked at the top of their own results.
In 9 of the 100 tests, Google claims they started seeing the site they'd manually ranked show up ranked #1 over at Bing.
3. Bing says it is one of 1000 signals they use.
We use over 1,000 different signals and features in our ranking algorithm. A small piece of that is clickstream data we get from some of our customers, who opt-in to sharing anonymous data as they navigate the web in order to help us improve the experience for all users.
4. Google’s engineer Matt Cutts asks
If clicks on Google really account for only 1/1000th (or some other trivial fraction) of Microsoft’s relevancy, why not just stop using those clicks and reduce the negative coverage and perception of this? And if Microsoft is unwilling to stop incorporating Google’s clicks in Bing’s rankings, doesn’t that argue that Google’s clicks account for much more than 1/1000th of Bing’s rankings?”
Looking at the hundreds of our client site results, we don't see that Bing and Google's search results are close enough. We also wonder, if clicks on Google really account for only 1/1000th of Bing’s relevancy, why not just stop using that data and reduce the negative coverage and perception of this? We will have to wait and see how Bing reacts.