Local game nerd Benedict Fritz nailed it with this one. I was going to include a quote here, but realized I wanted to copy-paste the entire thing, so just go read it there.
Benedict dscribes exactly what my experience has been. In the Drupal community in DC and the iOS community in Chicago, I just kept coming back and eventually got to know the core group really well. In the iOS community in Denver, I went to a couple events, but felt out of place and didn’t bother going back. It’s entirely possible that I might have gotten to know the group there just as well as I have in Chicago, but I submit that the iOS folks in Chicago and the Drupal folks in DC are both friendlier and more welcoming than the iOS folks in Denver were, at least the few times I went.
I’ve also been on the other end. Now that I know a bunch of people at the Chicago iOS events, I tend to spend most of the social time catching up with people that I only see once a month, and less time getting to know new people. It’s something one has to be intentional about, and be conscious of the fact that it’s important to welcome new people who might not come back if they have an unpleasant experience or two.