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The basic object was people's personal feeds, but FF added a "room" feature, around shared interests. Many of these worked extremely well. The best open science discussion for many years was in several of those rooms.
Facebook added many of these ideas (inc. the like button) after acquiring FriendFeed, but none of them ever seemed to work quite as well there; lots of details aren't quite right. In some ways it seems like a watered-down, rather more cumbersome and clunky version of FriendFeed.
huh, i was just thinking about this group interest idea earlier today. information entanglement? maybe i asked my inner oracle and found @paulg's question and @michael_nielsen's response simultaneously? then i observe twitter and there's my answer... 
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