This is as good a time as any to point out that the GREATEST advantage you've built into Hubski is the user-centric nature of the site. You have no moderation, you give utter and total control of the experience to the user, you do not impose anyone else's editorial over their experience, and you require a new user to successfully build out his own experience. I'm not saying it's perfect right now, but from a systemic perspective you have crafted an architecture that provides for far more customization and extensibility than Reddit or Hacker News.

Going invite-only is contrary to this philosophy. You're giving one user control over who he or she wishes to participate with, which means a random bystander needs the approval of a current user in order to interact with them. Effectively, I can influence who gets to talk to you and I don't think that benefits the community at the current time. It's not a lot of influence, I grant you, but it's a philosophical shift of direction.

Lost in the shuffle of the Great Mute Wars was my actual suggestion: Give me a preference that says "Ignore users newer than X days." I also asked for "Ignore users OLDER than Y days" because my explorations of Hubski benefit from atypical methods of exploration and I think an opportunity to see what week-old newbs chat about could be really interesting. Of course, when inundated by Reddit refugees, having a chance to say "ignore users newer than 2 days" allows the rest of us to see Hubski as we're expecting it without diminishing their experience one iota.

I think that you've done really well by putting the individual user experience first. I'm not sure that putting up a velvet rope will continue that tradition.