Google has gotten a lot of publicity about its complaint about Bing. There are some good comments here.
When you use Google Chrome, with its default Google search option, it spies on your browsing habits by sending your URLs back to Google. It does this, presumably, to improve its search rankings and advertising revenue.
Now Google has discovered that if you use the Microsoft IE8 browser, enable an option to send data back to Microsoft, and install the Microsoft Bing toolbar, then certain browsing habits are reported back to Microsoft for use in the Bing search engine. So why is this a problem?
I set the default search engine in Chrome to be Yahoo, just to cut back on Google spying. I hope Google publicizes this more, but a lot of people think that Google search results are based entirely on algorithmic Page Rank. In fact it is based largely on hand-tuning of favored sites, and on user spying. Bing is just playing the same game.
Update: This article details how Chrome sends info back to Google. Google says that it does not track what you type into the address bar, but, as you can see from the article, that is not true.