I'm not sending out RSVP cards either. So far, everyone (except for my bro) was RSVP'd on my site. I have also been communicating with my TA, as she updates me everytime someone books.
Now if people do not use her, and do not RSVP on my site, then I'm $crewed, but I'm hoping everyone follows directions =) Everyone has been so excited when they book, they have been calling and telling me...
I had our website on our STD and I'm also putting RSVP to our website on our invites.
We sent our STD at the end of January and are sending our invites at the begining of April. It's 4 months in advance, but I want to give everyone advance notice that it's near...
Hope that helps!