Irishwonder pointed me to his blog post on the subject of readability indices. He's referencing a nifty little tool that you can use on your own pages as well as comparing the readability levels of various SEO/M industry blogs (we're ranked 3rd behind SEOBook and Jim Boykin but ahead of Matt Cutts).

I'd be interested to see a large scale dissection of high ranking pages across industries and see if patterns crop up in the readability stats and measurements.