All search engines employ a ranking algorithm and one of the main rules in a ranking algorithm is to check the location and frequency of keywords on a web page. Don't forget that algorithms also give weightage to link population (number of web pages linking to your site). When performed by a qualified, experienced search engine optimization consultant, your site for high search engine rankings really does work, unless you have a lot of money and can afford to pay the expert. With better knowledge of search engines and how they work, you can also do it on your own.