Zed Shaw is one of the most original thinkers and prolific programmers currently active in Open Source. In 2006 he kick started the Ruby web application server market and continues it with the Mongrel2 server. He's an expert teacher and has taught over 300,000 people with his free book Learn Python the Hard Way. In this screencast he builds a code stats tool for tracking errors and warnings. But we think you'll appreciate most the conclusion of the project where he talks about the things he learned from using a previous implementation of a code statistics tool for a full year.