Danny Sullivan has a story about Google's claims that Bing copies Google search results. Google noticed that there's an rising overlap between the top results at Google and Bing, so it supposed that Microsoft was using Google's results to improve its search engine.
To verify its doubts, Google set up a smart operation. For the first time in its history, Google crafted one-time code that would allow it to physically rank a page for a certain term (code that will soon be removed, as described further below). It then created about 100 of what it calls "synthetic" searches, queries that few people, if anyone, would ever enter into Google.
These searches returned no matches on Google or Bing — or a tiny number of poor superiority matches, in a few cases — before the experiment went live. With the code enabled, Google placed a honeypot page to show up at the top of each synthetic search.
The only reason these pages appeared on Google was because Google required them to be there. There was nothing that made them obviously relevant for these searches. If they started to appeared at Bing after Google, that would mean that Bing took Google's bait and derivative its results.
This all happened in December. When the experiment was ready, about 20 Google engineers were told to run the test queries from laptops at home, using Internet Explorer, with optional Sites and the Bing Toolbar both enabled. They were also told to click on the top results. They started on December 17. By December 31, some of the results started appearing on Bing. (...) Only a small number of the test searches produced this result, about 7 to 9 (depending on when exactly Google checked) out of the 100.
Microsoft's engineers almost certainly thought that Google's results were pretty good, so why not use clickstream data from Internet Explorer and Bing Toolbar to monitor the results picked by Google users? It's a clever idea, but not when you're using it to unnaturally add results from Google. Bing's team says that they use "collective intelligence" to improve search results, so we can assume that a non-negligible amount of intelligence comes from Google. When you're including results just because Google does it, you're credulous Google too much and you implicitly admit that Google offers better results.