Jason Kottke asks an interesting question:

[H]ow does the broken windows theory apply to online spaces?

Kottke answers it in three parts: ownership, unchecked negative actions, and design. I think design is largely irrelevant to how a community interacts, but then I’m a technically-minded geek and don’t have much flair for aesthetics. The first two are, though, terribly important. Members of a true community must own their words, and abusive actions must not go unchecked. I personally have a policy on forums that I run: one person, one account. Catch someone running two accounts, and you confront them about it—publicly. The community has to know that they can’t game the system or be asshats, and multiple accounts per user is the most common form of asshattery.

As to the spam issue, I know that spammers check for success and pour resources into successful channels. That’s why I run Spam Karma and Akismet as a belt-and-suspenders approach to spam capturing on blogs I run.