Google Plus is a very impressive product, but in order to test it and not over-hype it, the company offered very few invites to the service when it launched yesterday. Press and a few others were allowed to enter up to 15 email adresses before noon yesterday and all of those people got Plus accounts by mid-afternoon. Accounts did not come with any allocated invitations, though, so it's been widely reported that there are no Plus invites.
Apparently that's not the case. All you need to do to invite someone to the service is to paste their raw email adress (I've only tested this with Gmail emails) into the "who to share" box and then send them something. A certain number of people per hour can get in from each current account holder. Thanks to Jennifer 8. Lee for pointing this out on Plus. Want an account? Add your email to the form below and we'll send out as many invites as we can right now. And remember: who scooped the story of Google Circles 3 months ago at SXSW? Oh yeah! Here's our review last night after a few hours of testing it: it's pretty awesome. Sorry, having Doc edit problems, I put a form below.
Update 1: It appears that I have run out of invites for the time being, just invited 500+ people within 20 minutes. But anyone who has an account can now invite some more people and I should be able to send more invites soon.
Update 2: Google has announced that invites are closed for the evening.