it's funny how they decide to give out invites.  i had an account for over a month and not one invite.  then one day i get one and i send it to my friend.  the next day after he opens his account and he's got an invite already.  luckily, the day after that, my account suddenly got 6 new invites!!  i'm not sure how they do it, but i guess you'll get some sometime.
btw, the invites are already given away so please don't pm me about them.