For real estate, it's location, location, location. For social networks, it's privacy, privacy, privacy...in conclusion, Facebook is doomed.
Macworld listed 5 things that Facebook can do to fight back against Google Plus. I think the article needs to be written and use the points commenters brought up as the place to rewrite the whole post and conclude that Facebook will soon face a world of hurt.
Because those points are the exact same thing that Plus or anyone can do can. What Facebook is unwilling to do is protect the privacy if its users.
Source: Macworld - most of the time, Macworld has great posts but honestly, don't waste your time reading this one. Nothing offered is a game changer