List accepted (and not yet ones) invitations
Keep track to whom accepted invitation and those who didn't yet.
When you send invitations to many people, you can't know for sure who actually accepted so you may want to resend invitations to your list of contacts (and again… And again…).
Nuno Carvalho commented
I am having the same problem here and I think it's very important to have a page that keeps track for the sent invitations, with an option to re-send the invitation. Thank you!