Email or not to email?

Whilst working on one of our weddings for spring 2010, we have been putting some thought into invitation etiquette with the bride and groom. The bride and groom would like to receive their RSVPs by email to keep things simple and organized but we have also talked about some guests like to have the opportunity to respond by formal paper RSVP. In the future, it may be nice for the bride and groom to keep these to look back on as memories of their wedding or is that just too sentimental in this day and age? Some people are choosing now to even send email invitations for their wedding and do away with formal stationary all together? Good cost saving and modern or a little to impersonal? Whatever you do, it must be the personal choice of the bride and groom and reflect their styles and personality. Have you had a modern style of wedding invite and what did you think? What about for other non-wedding events – would you be happy to receive an email invite and RSVP my email?