Do Crystal Balls Work?

In writing my analysis of various races around the country, I rely on several different websites, but none more so than the Cook Political Report, which has been producing prognostications for many years. Of course, a lot of "conventional wisdom" turns out not to be very wise, so I sniffed around to see if anyone had examined whether or not anyone had researched the past performance of Cook's crytsal ball. Joshua Green at The Atlantic had already done the math, which I am not very good at to begin with, and he shows that Cook has been right most of the time.