If you are interested in community formation and have an hour to spare you should check out this presentation by Seth Godin on Vimeo where he talks about the ideas in his book Tribes.
Here are the slides from the presentation:
Seth Godin on Tribes – SlideShare
Update – 13/12/08: As per Andrew‘s comment below the Vimeo embed is working now. Thanks to Andrew for posting the video online. See Seth Godin On How To Build And Lead Your Tribe. : Mixergy.com
I would have embedded the video here as well, but when I tried I got this message:
Seth Godin on Tribes–via Mixergy.com
Some “feature”! I’m not sure what Andrew Warner has against WordPress.com. At least Seth lets me embed his slides. 😦
Sean's Emerging... 
That Andrew is such a jerk! 😉
Okay, I fixed it.