That doesn't work for interest-specific communities. HTML5-ers, Java-ers, and haskell-ers will probably not talk about the same topics with each other as they would with other people that share their interests, as in their own interest-specific community.

Isn't that why on freenode, you have communities based around particular langauges? #java, #haskell, #html5, etc. etc? Not to mention social versions, like #haskell-blah and what have you.