I think

[XpierulesX]

If it's only a few people that's gonna be in CB I think i should be picked :D

[nsstrunks]

Everyone should have a fair chance at getting into the beta :P

And there's many different ways that they could send the invites out. At random (pick a random integer between 1 and the total number of accounts), GM favourites (though this wouldn't be fair), by the highest level players in Fiesta, etc.