This is my first thought as well. Google's pagerank analyzes the link structure of the web as one of the inputs to its search ranking. Apparently, Bing's toolbar analyzes page content coupled with user click behavior as one of the inputs to its search ranking.
These two things don't seem very different to me. Both of them are relying heavily on the value provided to them by tracking and analyzing the behavior of users on the web to drive search results.
Bing will be at fault if they specifically target Google. But if you consider entering a keyword and then click a link is essentially targeting Google search, then it only expose another problem, that is Google's monopoly on the search market.