Regardless of whether or not the "he stole my idea" story is real, I do think that he may have a good case that "Facebook" isn't trademarkable. When I arrived at college the year before Facebook the site launched, we received a dead-tree book at orientation that was called a "Facebook", and they had been a tradition there and at many other schools for a while. While Apple can trademark their logo, they can't trademark the word "Apple".