"Craigslist is not only gigantic in scale and totally resistant to business cooperation, it is also mostly free. The only things that cost money to post on the site are job ads in some cities ($25 to $75), apartment listings by brokers in New York ($10), and—in a special case born of recent legal trouble—advertisements in categories commonly used by prostitutes, because authorities encourage vendors to maintain a record that would aid investigators. There is no banner advertising. They won't let you join them, and at this price you can't beat them either."
http://www.wired.com/entertainment/theweb/magazine/17-09/ff_...
Usually, when companies get mad about scraping, it's because it's either bypassing the ads that make them money, or in rare cases bypassing a premium API. Here, PadMapper is doing neither.
In fact, if Craiglist is so committed to not updating their ugly website, why don't they just license out a public API, killing two birds (new monetization strategy and having a better interface for free) with one stone?