We have a core group of 11 regulars, plus some newcomers who may or may not become regulars. Having a decently-sized core group, means that we typically get newcomers from our pre-existing social networks (roommates, brothers, friends, etc), especially since we tend to hang out with other rationalist types anyways.

Our worry, in fact, is that we can't get too many new people involved at once, or it would change the dynamic so that we'd no longer be an explicitly LW group (i.e. if there were 2 new people for every LWer).

Something I've noticed is that the gender ratio at the meetups seem to be vastly better than the gender ratio on this site. (Latest big Yvain poll has 8% women, whereas our meetups always have about 33.3% women). I am very curious as to whether this trend is specific to our group, or whether this is true at meetups in general. I would be very appreciative if people responded with their own experiences with gender ratios at meetups.

Why I think this is: A recent survey showed that women were much more likely than men to find LW or HPMoR through social recommendations (such as friends). (Henceforth is anecdotal evidence) Also, from personal discussions, I've found that the women in our group have expressed a preference for learning about rationality in a social setting (such as the meetups) rather than reading a bunch of impersonal blog posts.

I think we are lucky in that our group has a handful of people who can at least fake extroversion. It seems important that there is at least one extroverted (or faux extroverted) person per meetup, to keep conversation going, keep people engaged, etc. From what it sounds like to me, meetups are much less smooth and more awkward when they lack this. I would also be interested in other people's experience either way with this.