I've built a number of private online communities over the years and have experimented with language around exclusivity and scarcity enough to know that it works well to draw interest where it was previously difficult to get people to pay attention.

I've often wondered why more startups don't try to build some sense of exclusivity to the sign-up process. Everyone is so focused on removing the barriers to sign-up and getting the user to improve their vanity metrics. Getting quality users by creating barriers to entry can be a tactic as well...