@people saying people won't leave Facebook, due to fleshed out profiles on Facebook.
Years ago I remember Myspace being the big social networking site, when Facebook released with a much cleaner interface. I watched people maintain duo profiles while they waited for their friends to convert to Facebook, and then once enough people moved, they stopped using Myspace altogether.
The interesting thing about this, was that Facebook offered very little over Myspace back then, in terms of functionality. It had LESS, actually. What it did have, though, was a cleaner interface, and the feeling that the site would move in a more user friendly direction with new features. Oh, and possibly most importantly, an escape from many of the annoyances of a Myspace interface that was trying too hard.
I'm somewhat annoyed, honestly, by how Facebook takes this stance of how it's sooo unique, and how they're sooo innovative, when they didn't really invent anything at all. Given the history of social networking sites, they should be shaking in their arrogant, lazy boots, because if G+ has the superior user interface, people will start moving out in droves almost immediately. And lets not rule out the "I just don't want to be annoyed by unnecessary BS" factor as well. I'd switch just so I won't ever see anymore Farmville / Bejewelled crap.