Things are always in the last place you look because once you find them you stop looking. That well-known idea led Tom Costello to research why loyalists would want to leave Google for Bing, so he took a survey of 400 queries, the kind that might prompt people to switch search engines.
Costello provides stats on overlap, differences and the ratio of spam in results, along with notable differences in rankings. He writes that people often claim search engines rank "sufficiently similar," so you can't tell the difference. But a well-designed test can tell them apart, he writes. He also looks at whether Bing is using any new signals, beyond what are usually used in search engines.