At the risk of stating the obvious, Twitter is a directed graph (one-way follow), while Facebook is (mostly) undirected (two-way follow), I have to friend you a

At the risk of stating the obvious, Twitter is a directed graph (one-way follow), while Facebook is (mostly) undirected (two-way follow), I have to friend you and you have to agree. Twitter is more for the digerati, Facebook is more for the masses. Facebook has more of a mission to capture and monetize all your social/personal info, Twitter is a little more narrowly focused.