I wish DW/LJ had some sort of "+1" / "thumbs up" / "upvote/downvote" system. Or, really, ideally, I'd like a bunch of smily faces along the bottom of a post so you can quickly click the "sympathy" face, the "laughing out loud" face, the "angry" face, etc. to express appropriate sympathy with what someone has said. I find that people (including me) often read posts, regardless of length, but don't have anything substantive to add, so they don't say anything... which adds to the "shouting loudly in an abandoned mine" feeling.

Beyond that, though, DW (and, to a lesser extent, LJ) have privacy settings that make them completely indispensable to me. FB is completely pointless to me, what with Mark Zuckerberg deciding whenever he feels like it to destroy people's privacy. G+'s circles seem slightly better, but not by much. For now, DW is my main social media platform, with LJ a close second and everything else a distant third.