Ranking formulas are secret and always changing
SEO is a complex task because the criteria used to rank sites is a secret. The ranking formula used by each search engine is that company’s most valuable intellectual property, and so they don’t reveal it. There are around 200 criteria used to rank sites and the exact weight given to each item is never revealed. To make matters even more complicated, the weight given to these items changes regularly to deal with advances in search and optimization techniques. As a result, adhering to best practices is always going to get you better long-term results than flavor-of-the-month SEO.
[May 19, 2009]