There are so many internet marketing strategies that have been successful for a long time, but now search engines like google, yahoo, and ninemsn just to name a few have been blacklisted or now described as blackhat strategies.
The most notable worst internet marketing strategy every could be awarded to the technique called keyword stuffing.
According to wikipedia: "Keyword stuffing is considered to be an unethical search engine optimization (SEO) technique. Keyword stuffing occurs when a web page is loaded with keywords in the meta tags or in content. The repetition of words in meta tags may explain why many search engines no longer use these tags".
More info go to: wiki keyword stuffing
The most notable example that I have seen regarding this internet marketing technique came from an article by matt cutts describing a particular site about a guy called alex chiu, his site is basically about an immortality site. His website had a text box , that was stuffed with alot of keywords, solely used for the search engines. Basically useless for potential client or the end user.
Example 1:


Google did ban Alex chius's website, because it did not abide by google's webmaster guidelines which states " Don't load pages with irrelevant keywords".
If you would like more information about this article please go to:
Matt cutts keyword stuffing blog
NO.2 LINK FARMS
This is another strategy that has been utilised for many years, by many blackhat SEO's, trying to build their page ranks and a common use of link building.
Link farm is defined as a website containing many hyperlinks, especially one designed to increase page ranking.Although some link farms can be created by hand, most are created through automated programs and services. A link farm is a form of spamming the index of a search engine.
Defintion from wiki link farm
Link farms where utilised to get income from selling links. This still exists and there are many sites offering packages to submit to 2,000 - 10,000 links instantly. The obvious problem with this advertisement is that google is alot smarter these days and would observe the website that a webmaster could not gain 10.000 links in a matter of 5 minutes. This type of technique was used frequently, now is basically a no go zone to many SEO's. Due to there has been many sites being banned by google.