> A meetup to discuss Ruby on Rails or something is all about the subject of the meetup. Most are there just to talk about Rails and get help with a bug, not to make close friends.

You can sometimes make friends in such settings if they're regular enough, informal enough, and smallish groups. I initially met one current friend via the SF Wikipedia meetups, for example. But they have a somewhat deliberate "social outing" tone, where it's expected some Wikipedia business will be discussed, but not in any organized way.