SEOMoz: What Makes a Good Web Directory, and Why Google Penalized Dozens of Bad Ones

This article by Rand Fishkin of SEOmoz is pretty interesting, I especially like the "Twelve Attributes of Obviously Manipulative Directories" list. Its a good guideline for looking over the quality of directories you are thinking of submitting your website to.
What Makes a Good Web Directory, and Why Google Penalized Dozens of Bad Ones