Assume an ideal situation: Essentially the same content or link is cross-posted to Facebook, Twitter, Google+, LinkedIn, Tumblr, etc., but it’s (a) relevant to each audience and (b) adjusted to fit best within each network. No #hashtags or @usernames in the Facebook post, no fb.me links in the Twitter post, link previews in Google+ or Facebook, etc.
Update: Some discussion over at Speed Force.