Such a riveting article. Something as ubiquitously mundane as the People You May Know feature being the thing that helped break Facebook's plateau is quite curious.
I found this particularly enlightening about how Zuckerberg (and perhaps, I've been suspecting lately, Jack):
“We don’t view your experience with the product as a single-player game,” he says. Yes, in the short run, some users might benefit more than others from PYMK friending. But, he contends, all users will benefit if everyone they know winds up on Facebook. We should think of PYMK as kind of a “community tax policy,” he says. Or a redistribution of wealth. “If you’re ramped up and having a good life, then you’re going to pay a little bit more in order to make sure that everyone else in the community can get ramped up. I actually think that that approach to building a community is part of why [we have] succeeded and is modeled in a lot of aspects of our society.”