Thinking out loud: If the issue is simply video, one could pretty easily run an IRC meetup. It has the advantage of still being somewhat "real time" and thus something you could block out an hour or two for a weekly "meetup."

If you want to avoid real-time entirely, then a forum or mailing list ought suffice. I'd point out that LessWrong is already effectively a forum, so I think you'd get a lot less out of this.

All of these, including the video conference, probably also run in to scaling issues unless you have a very good organizer and a crowd willing to go along with it. I'd expect small groups of 3-6, splintering as needed, would probably be best?

I suppose mostly it depends on what you're looking to get out of it, and why the main LessWrong site doesn't suffice.