Wired has a great online piece on Craigslist that gets deep into why Craigslist is the way it is.  I've followed Craigslist for a long time now, so there was nothing new that surprised me, but if you don't understand Craigslist's dynamics then this article is an eye opener. 

Here's a quote that I've known for some time:

"Think of any Web feature that has become popular in the past 10 years: Chances are craigslist has considered it and rejected it. If you try to build a third-party application designed to make craigslist work better, the management will almost certainly throw up technical roadblocks to shut you down."

I built NotifyWire.com knowing this was their attitude.  For every feature that get's added, I think, "OK, if I was Craig, what roadblock could I throw up to kill this?"  At the end of the day, there is really nothing Craigslist can do to shut down NotifyWire's Craigslist search tool.  Not to get too technical, but NotifyWire is essentially a fancy, distributed, RSS reader and web browser made specifically for Craigslist. 

Soon, NotifyWire.com will expand to include simple to use features to eliminate SPAM and SCAMs as you reply to ads or post your own.  Again, with these new features, I've also built it in a way to ensure we can't easily be shut down by Craig.

It's not that I want to be stand-off-ish with Craigslist, but this is the reality they've created.  On the plus side, they've created a market for someone willing to play this cat and mouse game.