I see the number one problem with people / new sites / and under estimating MSN. People find that if they create a site and it ranks well right off the batt to leave it as is and never change it. Websites and
SEO is not just a one time thing it's a all time thing, never stopping and always adding more and more content.
Remember that content is kind, the more you have the better. And yes adding a (S) to any of your keywords does make a big difference.