Definitely some good points being made. SEO can be successful if done properly, but as Deaning pointed out, winning in SEO and on the web in general is all about site relevance. If your site is relevant to the information people are searching for then you will have stronger conversions, if you are spamming search engines, then conversions will be much lower, and Google will kick you out for the spamming one day.
Google is very concerned about relevance, it is their lifeblood and the reason they are valued at over $80 Billion. If they aren’t returning results relevant to a person’s search, then that person will go elsewhere to do their searching and Google will be out of business. The lesson for marketers is to create a highly relevant site, market yourself for what your site offers, not generic keywords and you should do fine.
Just don’t forget that content is king.