Coming from a technical programming and IA background, I’m well versed in the science of SEO and how important it is. I go crazy for this stuff and it drives me crazy when it’s not considered as part of the design of a site.
Stephan Spencer has a great article over at SEL on The Science of Scoring Your SEO and it’s definitely worth a read.
SEO is a moving target, one that is heavily dependent on algorithm shifts, site changes/updates, the competitive landscape in which one operates, etc. As such, you must continuously monitor and evaluate, ideally with an automated tool. In fact, such a tool is mandatory if you have a large site and you want your SEO activities to be scalable. With this monitoring in place, a page element (like a meta description) that goes AWOL can be flagged and the issue addressed (e.g. internal resources deployed) much faster than would be otherwise possible. Even better if the webmaster can be flashed warnings prior to making site modifications that will be detrimental to SEO.