I wasn't planning on doing the whole wedding-website thing, but I've kinda gotten sucked-into doing it and have set one up through theknot.com. My question is do I have to give my guests the option of RSVP-ing online, or can I "require" them to snail-mail their response-cards? (I don't want to waste money on response-cards and postage if everyone's going to RSVP online.)