SEOChat has an interesting article on Google Algorithms, explaining the techniques used by the search engine.
It explains that you should write naturally so that related words and not just words with the same meaning should appear. So if you were writing about gardening services you would use words like grass, plants, ground, weeds, etc. Not just garden, gardens, landscaping, landscaping, etc.
It then goes on to explain about Link Analysis, the supplemental index and human reviewers. Worth a read if you want to ensure your site stays top on Google.
Google Analytics
search engine, google