To perform search engine optimization on a site or for a company is not as simple as waiving a magic wand, changing some items within a person's website and voila - the site is now ready to rank number one in Google. SEO is much more complicated than that and has only become more and more complicated as time goes by and the Internet has grown more sophisticated.
According to SEOMoz - responsibilities of an SEO Strategist have evolved since 1999 and now in 2011 are all of that from the past plus some. They include:
Add to this 2011 responsibilities:
As you can see, the workload is tremendous and the amount of research equal. If you are looking to optimize your own website, be prepared. If you are looking to hire another company, realize the reason it isn't cheap is due to the shear amount of research and work. And, if somebody offers to provide SEO for you for little to no cost, especially if they are from foreign countries, know that you get what you pay for.