Many people preach their own brand of search engine optimization as the absolute truth.  Ask 10 different SEO companies a question, and you will often get at least 8 different answers.

Who should you believe?

You should use the advice of someone you trust completely.  Someone who has provided good results over and over, and who uses their own advice on their personal sites.  Sean Burns is someone I trust completely.  He gives excellent advice, and often shows you how search engine optimization advice that is being preached as gospel is actually useless. He's one of the "good guys."