I attended a day long workshop run by Lou last year which covered this and a few related topics and have been sharing his report card with anyone who'll listen ever since.
A must read article for all web managers (and their managers).
Stop Redesigning And Start Tuning Your Site Instead - article by Lou Rosenfeld for Smashing Magazine
My previous post about Lou's session includes slides which are worth a look if you want to learn more beyond this article.
Avoiding your next site redesign (Blog post from October 2011)