I have noticed that given how much I identify as a rationalist, how much I have in common with the community here, how important I consider it, etc. I have surprisingly little instant in group identification with community members compared to other online communities. There seem to be an aspect of social involvement that LW does bad at. And there is one thing lacking that to me seems the obvious first suspect; the lack of of-topic unstructured chatter.
What I do when I feel that I identify with some continuity online is in fact not usually the thing the community is ABOUT. Instead, it's the things that grow out of the sides; forum games, members art projects, photo share threads, fanworks. I can speculate on why this happens this is so, but it dosn't seem very useful at the moment, I'm not highly confident on any specific theory, and most will probably find it fairly obvious anyway.
LW, however, has no real room for this. Even in the discussion section, things that are not reasonably on topic will be punished with negative karma. Now, this is obviously needed, but one must still recognize there IS a prise to being so structured and focused on a single goal when humans naturally tend not to be. Look for third options.
Now, I have a specific solution in mind, but I'm going to hold of on proposing it and see if you come up with something better before I post my idea.
EDIT: My suggestion has now been added in the comments, please check it out.
I'm not really sure how obvious the need for a more engaging social community is. I suppose it depends on exactly what one sees the purpose of the site to be. The focus I'm mostly interested in is developing solid resources for good reasoning in various areas and reaching a large and diverse audience with them.
I'm thinking the resource developing part as basically something like how a science journal works. People come up with stuff, other people question it, and stuff gets hopefully iterated into better stuff. Good science journals generally have some balance between adversity and agreeing to common conventions. When people form a tight social community, they might start polarizing against the outside and producing groupthinky junk instead of argument-hardened stuff.
Also not sure about the community aspect for the audience thing. Basically the site should have some number of people writing useful posts, some more active participants giving feedback and having discussions, and a large number of readers who can hopefully make use of the stuff. It'd also be very nice to have people who actually do stuff on the outside participating, either doing serious scholarship or real-world empiricism, and distilling ideas from there into site content. Unfortunately this favors people who do a lot of stuff outside the forum and bring in the outside insights, while there's a lot less main content to be made by just puttering around with in-forum stuff.
So cultivating a somewhat dry atmosphere might actually be an advantage, if it could be used to encourage people to bring in high-impact content based on research outside the site, to maintain the sort of constructively adversarial air useful science tends to emerge from and to keep the general tone sufficiently broad that the content is accessible to a diverse audience.
Is a close knit community, as opposed to just being a reasoning tool, part of the purpose of LW? Considering his support for the various IRL rationalist communities, many things in ""The Craft nd the Community sequence, and general temperament, Eliezer certainly seems to think so.
But yes, the risk of groupthink, contaminating the Science journal type functionality of LW, and so on are indeed important dangers that any solution to the problem must address.