Up to now, Pinterest has been by invitation only. Even so, it had 10 million users within 9 months of it’s launch in 2010. The latest news is that the invitations are no longer need and anyone can register as a user.
From the BBC article, Pinterest opens site to all, stops invite-only policy
“They’re one of the main sites that serve the so-called social collectors, people who like to curate information across the web,” said Forrester Research analyst Darika Ahrens.
“What remains to be seen is what happens if they start to commercialise – how they’re going to do that and if they do it in a way that’s not going to alienate their users.“So far, they have tried a number of different methods such as using monetising links that bring in a revenue share, but they stopped that.