Bing announced last week that they are venturing into personalized search results. Yes, they have announced a partnership with Facebook to personalize results, but those are within box elements on the page, not tailoring the actual results you get.
This new announcement is Bing's first real venture into personalizing the actual search results based on two personalization factors.
(2) Previous Searches
Bing admits some of these personalization are "relatively simple" but they can make a huge difference. I should note, Google has been doing these personalization techniques for years.
(1) Location: If you search for something that may have local intent, such as [pizza], Bing will use your location to tailor local pizza results.
(2) Previous Searches: Bing is now presenting relevant website based on an individual's previous searches. For example, if you are searching for travel related keywords and then search for [jfk], Bing might understand you are looking for the airport as opposed to the President.
There has been no forum discussion on this until yesterday and that forum discussion is actually referencing the old Facebook announcement.
Forum discussion at WebmasterWorld.