Thank you, Jessi Hempel of Fortune:

Pinterest emerged as the fastest-growing website of all time. In March the site registered 17.8 million users, according to Comscore, a 52% jump in just one month -- and it isn't even open to everyone (would-be "pinners" must still request an invitation to join).

I also liked this paragraph about curation:

While Pinterest's Palo Alto digs feature a poster with the words move fast and break things, a mantra at Facebook, Silbermann talks about Pinterest the way one talks about a fragile heirloom. "When you open Pinterest, it should feel like someone has hand-made a book for you," he explains. "Every item should feel like it's handpicked for you by a person you care about."

Move fast and break things? Very Facebook.

Hockey stick growth and a guarded community? Very Instagram.

Hopefully Pinterest won't sell out.