To the person asking how to use invites: on the front page it should tell you, just above where your friends status updates appear, if you have invites and how many. There should be a link right there that will take you to a form where you can put in their email addresses and it should send them an email inviting them to sign up. as to the original question, I imagine we might get more invites after the next big update has been out for a little while and the hubbub from that has died down
@ICountFrom0 I think that used up your invites as well, but was removed? I haven't seen it at least.
@Everyone else, I just kinda doubt we'll get anymore invites period! Why would they want more players to deal with :P? They cited scaling as a reason for going back to beta. They didn't have time to work while scaling the game to its growing player base. Just my two currants, as they say!
Liza: They used to give us more invites periodically during the previous beta. They seemed fine expanding the player base slowly while working on big things. I wouldn't rule out getting any more during this beta phase (they are redoing beginner tutorials and stuff and would need new players to test it), but I wouldn't expect it either. It is just one of those things that will happen if it happens.
About the Facebook invite process: They had said in the past they wanted an email invite system rather than the Facebook one, as not everyone is on Facebook that would want to play, so I guess they implemented it since the last time I invited someone. Facebook used to be the only player-invites-player system (through beta anyway).