1. It's not obvious what you do that's special. There's probably some secret sauce in figuring out who I might have forgotten, but you don't tell me what it is.
2. It would be useful to have a walk through or screencast or something showing how it works. For example, does this thing just make lists, does it manage invites, send emails? No idea from the site.
3. I won't use sites that insist on a Facebook login.
Also, as jgrahamc said, work on your message. It's not clear how much work is involved, maybe a step-by-step explanation. How are you sending those invites? What's special about your app? Do I have to pay anything?
1. I didn't want to add too much complexity to the app by going into details of advanced Social Network Analysis, but I'll think about adding details.
2. Good idea, I'll work on a screencast/walkthrough
3. I understand that, but I have no other solution: having access to the user's facebook friends is an absolute requirement for the app to run.
Nevertheless, thanks for your feedback.