Aaron Wall, founder, SEOBook.com
Myth #5: Keywords need to appear everywhere
A popular myth (brought on by people reading old SEO information that is not relevant to the current marketplace and optimization software that was programmed many years ago) is that you should put your keywords everywhere to rank as best you can. The truth is that Google's current relevancy algorithms favor more natural writing that includes a more diverse and realistic set of text with more variation in it. Some common variation strategies include using both the plural and singular versions of a keyword, changing the order of words in a phrase and adding relevant modifiers to page titles and headings.
Four or five years ago if you wanted to rank for "credit cards" you would put that phrase in your page title, in an H1 tag on the page, and in most of your inbound anchor text to that page. If you wanted to rank for the same phrase today, you might put a modifier word or two in the page title, opting for something like "Compare Credit Cards Online." Within the page copy the heading might be something more like "Apply for a Credit Card Today." Rather than focusing on the core phrase, this strategy still gets you decent coverage for it, but also helps the page rank for a much wider net of related keywords, and it makes the page much less likely to get filtered. You should also mix up your anchor text as well, if possible. If every link to a site has the exact same anchor text it doesn't look natural.
In addition to Wall's SEOBook.com site, he has also launched the SEO Training program to help interactive marketers better understand SEO.