What address are you listing on your RSVP envelopes for guests to send reply cards to? Most of my engaged friends seem to be sending to their mother's house, however my mom lives far away and so does FH's mom. I would send them to my house but our mailperson frequently mixes up mail and puts it in the wrong box (one of those central apartment complex boxes.. ugh).
Part of me doesn't want to send anywhere else because I think it would be exciting to run out to the mailbox every day to find out who is coming!!
Where are your RSVPS going??