Bing closed down Bing Tags on June 14, 2013. A Microsoft spokesperson told us:
We can confirm that beginning on June 14, 2013, Bing Public Tags were no longer available and all existing tags were removed from Bing.
Most search engines are constantly testing new features, removing failed features and trying alternatives out all the time. It is not surprising to see this feature go away.
What Was Bing Tags?
The feature allowed you or your friends to “tag” web pages and documents in Bing’s index as being related to you or your friend. The purpose was to make the search results for you and your friends more personalized as well as richer.
The results looked like this: