Earlier, I realized that I've never given credit for one major influence on craigslist, and myself in particular.
A few years ago, I read The Cluetrain Manifesto which has a great deal of good stuff in it.
It talks about speaking with a corporate or business voice, as opposed to a human voice. The former is exemplified by sites you see with lots of happy, clean people, and the site says little, and they don't answer your emails. My intent is that craigslist exemplifies the "human voice."
The book has other great stuff, including the observation that markets are conversations.
I'm not doing it justice, so please start with the link above, and whoever has my copy, please return it.
David Weinberger, one of the authors, continues to comment in this regard, and I recommend his blog