They did it by being passionately, single-mindedly, ferociously committed to enforcing one rule: "Be Friendly."
Not that you can't have a huge community without that rule... slashdot is the perfect example. But if you're trying to inspire passionate users, I believe that enforcing a "Be Friendly" rule can be one of the best moves for long-term growth and retention of the community.
This sounds so simple, and yet I think this idea of being friendly is often overlooked. Take Lesley's post about being blasted for her comments on a blog.
As organizations with moderated lists, a policy of friendliness might be possible. But how do we establish such an environment in our own blogs?
People don't seem to feel a need to be friendly anymore. Not everyone, of course. I have to say that everyone who has commented on this blog has been very friendly. But I know not everyone is so fortunate. It is really too bad.