When is comes to trademarks, there's really no such thing as an intrinsically generic term. A term can only be generic as it relates to a good or service. So the term "facebook" is generic as it relates to "a reference book or electronic directory made up of individuals' photographs and names," but not necessarily as it relates to other things, like the modern social network. Under the framework we use in the U.S., "facebook" is probably a suggestive mark as it relates to social networks, which means that it deserves instant and relatively strong protection.
I've described the framework here: http://notmylawyer.com/post/248307917/choosing-a-valid-trade...