Exactly, they could just observe what user clicks after search (on any search engine, including Bing) and use it as a signal.
If that is indeed the case, then they are not copying results from Google, they are just tracking users' choices to improve position of interesting results on Bing. Personally, I don't see anything wrong about that.
Keep in mind that in Google's experiment, they always clicked on the first result, which is probably why their result was send to Microsoft and that the experiment "succeeded".
needn't even be limited to "what user clicks after search" could simply be "what user clicks"
They're trying to link Content A and Content B, where "Content" includes page content, URL(including GET string terms), and various other factors. Could happen on every page.
Google-fans then tend to get a bit knicker-twisty about privacy implications, but first I dislike that line of argument as it confuses the issue (what are we mad at, the copying or the privacy? Oh I know, we'll say copying and when someone rebuts that we'll start whining about privacy), and secondly, as patio11 eloquently said: Google doesn't really want to get into a heated discussion about the evils of a search engine knowing everything you've ever searched for. Stones, glass houses, etc. ( http://news.ycombinator.com/item?id=2165682 )
How long would it take for Microsoft do stage a similar trap for already installed Google toolbars? The fact it hasn't been done is a good indicator they couldn't.
If that is indeed the case, then they are not copying results from Google, they are just tracking users' choices to improve position of interesting results on Bing. Personally, I don't see anything wrong about that.
Keep in mind that in Google's experiment, they always clicked on the first result, which is probably why their result was send to Microsoft and that the experiment "succeeded".