How effective is school choice?

As I write from Arizona, the land of school choice with a charter or private school on every corner, I was interested to read this piece (largely ambivalent about school choice) and the blog responses (largely supportive of school choice).

http://freakonomics.blogs.nytimes.com/2007/10/04/more-evidence-on-the-lack-of-impact-of-school-choice/#more-1938