1. Keybase offers a way to read and send messages via PGP, which can be decrypted and encrypted by anyone. It's also a way to verify who's who if it's staked, which is useful in large numbers of bitcoin being transferred. Many uses for it.
2. I need an invite because I'm planning to sell things on this forum, and I'd like a way for my customers to verify that I'm me via PGP. I'd also just like to be able to stake my pgp on
https://bitcointalk.org/index.php?topic=1159946.0, since I have big plans for myself and I'd like to stake it; if somebody ever hacked my account, I'd be able to sign a pgp stating that I was hacked, and I'd be able to shut it down.
I'd definitely share my invites wisely if you gave an invite to me, if I ever saw somebody that wanted one, but didn't, and had a good account, I'd give him an invite.