Would appreciate it if you get an invite to also invite other people!

Click the grey "Share" button at the top right of the screen and type in a random message and add emails below it. Don't know if it's intentional or not but this invites people to google+.

edit:

Looks like ONLY *gmail.com accounts work. Google Apps does NOT seem to be working.

Also, people are getting my invites but getting message "temporarily exceeded capacity" so who knows if they've now disabled this.

edit 2: I've invited ~25 people in 20 minutes. New people are getting their invites but are unable to log in, so looks like it's either disabled for me now or disabled for all. If you've joined, please go through this list and invite other people!