Why do you need to be "invited" to Pinterest?

[Taylor]

My friend told me about it and it sounds cool so I went to go sign up. I had to apply for an invite. I got this e-mail:

Hi!

Thanks for joining the Pinterest waiting list. We'll be sure to send you an invite soon.

In the meantime, you can follow us on Twitter. You can also explore a few pins.

We're excited to get you pinning soon!

- Ben and the Pinterest Team

What is that? Why can't I just sign up and join and start making my own sets?

[faithfulstation616]

To prevent your account or others' accounts from being hacked. It's a safe way to log into the site and be confident in it. It is also a way for the site to get more users.