Ever hear of Latent Semantic Indexing? It's a concept you should familiarize yourself with if you're trying to drive visitors to your website. In layman's terms, the concept basically means that the search engines analyze all of the text on your web page - not just your keywords or key phrases - to determine the relevancy of your page.
The search engines are definitely getting smarter and more capable in "reading" a web page and determining what it's actually about. They are no longer looking for a simple keyword - so factors such as keyword density and keyword positioning are losing importance in your ranking.
The most effective way to address latent semantic indexing is by writing for people, not for Google. Use natural language, write as if you were speaking to someone, don't try to force keywords into the conversation just for ranking purposes. Be sure to mix your anchor text and sound as "human" as possible.
Have you started using LSI on your pages? Have you noticed a difference in the amount of traffic on your web site or the length of time people are looking at your pages? What is your experience with it?