Just to clarify to guess123 and anarchy, you do not get "unlimited" invites. I have not gotten any yet to distribute, but from what I've heard, you get a certain number to distribute every once and a while. If there were "unlimited" invites, then there would be little point in keeping GMail in its beta stage. The way Google does it, they control how many invites can be sent. After an invite is used once, it expires and cannot be used again. Invites also expire after three weeks of creation.