I am sure I'd have more users signed up if anyone could sign up. But I wonder about the quality of those users. Invited users feel they've earned something I ho

I am sure I'd have more users signed up if anyone could sign up. But I wonder about the quality of those users. Invited users feel they've earned something I hope. So they in theory should be more likely to fill out their profiles and participate in the site. Making the site invite-only also solves a lot of issues, spam links chief among those.