I hate to play devil's advocate, but that kind of crap is the reason Facebook apps exploded. You don't get viral growth without supporting friend-spam.
That's a pretty good point, but requiring it for signup seemed a bit much. It was more than "now invite your friends."
It's actually not required for signup. You would still receive coupons for free up to a face value of $5 (which is the vast majority in volume).
That was an incentive to foster virality, but your comments are very much appreciated.