Slashdot, which bills itself as "News for nerds. Stuff that matters," is one of the oldest and most influential communities of interest online. It operates with a rough egalitarian focus I envy; site users rank each post 1-10 based on perceived usefulness, and the readers can sort by telling the site, for example, only to display posts ranked 7 or above.
And so when one of the Slashdot founders speaks, people interested in online communities ought to listen. Rob Malda, known to Slashdotters as CmdrTaco, tells the New York Times he's worried about the sites where "the wisdom of the crowd" becomes "the tyranny of the mob" instead. Have a look over at the Times' technology blog, Bits.