"A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation."

http://en.wikipedia.org/wiki/Rule_of_thumb

Predictable is that craigslist seems to have some vendetta against external web apps, and you showed them a big data hole they had.

I'd ask Craig again on Twitter about the Pipes thing, he's better at responding to tweets than emails sometimes. http://twitter.com/craignewmark