My initial thought was that this idea sucks - would you want to be remembered as the couple who sent out facebook invitations because you were too broke/tight to do this properly, this once-in-a-lifetime event?

But then, could your suggestion be cast as a couple making a statement to reduce paper usage? And if enough couples do this, what kind of dent could it make on aggregate?

Pros:

- electronic invitations mean no paper, no postage.

Cons:

- chances are, people will print out the invitation and directions.