I heard an interesting term today that applied to the evolution of search engine technology called latent semantic analysis. The application of latent semantic analysis applies groupings of terms or variables to a concept, rather than a more traditional one-on-one relationship.
Although the technology has its flaws, it appears to be the next wave in the evolution of search engine technology. No longer will the Googles and Yahoo!s of the world be dependant on keyword density or incoming link anchor text, but rather on the concepts and information of your website and those of websites that point to yours.
Ultimately, this is just one more argument against trying to game search engines for higher rankings. Those wishing to sustain their websites over the long hall should focus on providing quality, useful material for their audience in a way that is easy to understand.
For more information on latent semantic analysis (LSA) here are some good resources: