I'm not doing a formal invite either. Im sending out STD soon (as my wedding is close to yours 4/23/11) and plan on sending out a little newsletter around the time invitations are out. I, however, have a wedding website where people can RSVP. I did see someone's response above that said people didn't go to the website, but I think in this day and age, everyone 1. forgets about the invite 2. looses it or 3. didn't remember to send the RSVP in the first place (with a formal invite). Almost everyone is online these days, and I think that's the best way to reach people. So, this is what I'm doing...hope it works for you as well...Good luck!