I have been optimising websites for over 6 years now, and it really is one industry where life long learning is paramount. I am not a website designer, I just optimize and I only just manage to keep up with the ongoing changes by Google, Yahoo and the other major search engines.
As the main search engines keep updating the spiders (robots) they deploy every day, it's important to know what they like. Also, it's just as important to understand what they don't like. Either way, I keep reading and posting and interacting with other specialists in this field, and that's why I'm staying up the rankings.