This is a technique used by website/blog owners to increase their pagerank..but this is often temporary and not preferred as this is compared with a spamming technique.
It just aims in atrracting the crawling methods of google spider.Search engine avoids those sites with use this technique.
Techniques like keyword stuffing(just including the compony/service name in possible places without any definite meaning),unnatural backlinks(creating links by paying money/illegal method)
It only focuses on ranking and not on the end user...hence it is often like a mirage wherein if people access the site they will soon have an idea that the site is spam. Service providers like http://www.thewebpole.com/search-engine/seo-services.aspx?ci=1800&prog_id=447401
provide Search Engine Visibility Service through which they help the user to get the desired pagerank through their legal and ethical ways.