A little over a year ago, Microsoft launched this campaign named the Bing It On Challenge, which was basically a blind-search taste test pinning Bing against Google, while removing the branding.
Ian from Freakonomics reports that the challenge was not just a "little fishy" but he feels Google may have an "deceptive advertising claim against Microsoft." He details why in his post at Freakonomics.
Matt Cutts, Google's head of search spam, shared this on Google+ and added some more color to his own thoughts on this challenge.
I have to admit that I never bothered to debunk the Bing It On challenge, because the flaws (small sample size; bias in query selection; stripping out features of Google like geolocation, personalization, and Knowledge Graph; wording of the site; selective rematches) were pretty obvious.
It is funny, because when I posted a poll on Who Won In Bing It On Challenge? 60%+ said Google won.
Anyway, well worth a read when you have time.
Forum discussion at Google+.
Update: Here is a statement from Microsoft PR, and also make sure to check out this comment from Microsoft's Matt Wallaert.
The professor’s analysis is flawed and based on an incomplete understanding of both the claims and the Challenge. The Bing It On claim is 100% accurate and we’re glad to see we’ve nudged Google into improving their results. Bing it On is intended to be a lightweight way to challenge peoples’ assumptions about which search engine actually provides the best results. Given our share gains, it’s clear that people are recognizing our quality and unique approach to what has been a relatively static space dominated by a single service. - Attributable to Matt Wallaert, Behavioral Scientist, Bing