We view it as an over all promotion strategy. It just makes sense that you would want your business listed and mentioned on as many good sites, and sites that are relevant to your business, as possible.
On site SEO is just the practice of making your site usable, and interesting.
Spend a moment viewing the Google video on our search engine optimization page and you will get the best over view of how Google ranks sites I have ever seen, in a few minutes.
See it here Denver Search Engine Optimization, Google video http://www.salesjumpstart.net/Searchengineoptimization.html