Is there a relationship between the link profile and what the site’s or page’s max keyword density before the page starts experiencing a filter? It appears to me from having worked on many sites over the years that I’ve observed sites being assigned a “penalty” or filter of +20-50 positions when the page crosses over a certain keyword density, many other SEO experts have also observed this behavior as well. But I’ve seen the very same pages also climb back up to their previous position when the link profile of the site has had current activity. My theory is that the search engines raise the allowed keyword density of a page as it appears to be more authoritative and has a stronger profile. This would make sense as you wouldn’t want to filter a very popular site because they used their keywords too much accidentally, but you would probably want to filter out an unpopular site that appears to have a much higher keyword density then it”s competing sites, at least that’s what I would do if I where Google and esp. since Google looks beyond just the number of occurrences of words or combination of words but looks for a “theme” on the page with LSI Latent Semantic Indexing, Latent semantic indexing allows a search engine to determine what a page is about outside of specifically matching search query text.
So with this in mind, I think it really makes sense then to look at other competing sites in your market and make sure you don’t go over their keyword density for any one particular word and make sure you’re using variations of your main phrases and not being overly focused on one phrase esp. if you have a weaker link profile. Also you’ll want to monitor your rankings closely to watch out for any sudden big dips that came out of a page being edited, we monitor all of our critical pages and phrases and we get alerts if something has changed suddenly for not apparent reason other then some page text changes.
So in essence, make sure to use a wide array of related phrases that are closely related in meaning, and that goes for on page, off page SEO factors. Again this is a perfect example of how the search engines are getting better at filtering out low quality sites, and how Google should really be called a “Quality Engine” vs. a “Search Engine”, as their goal is to return the best content possible to the person searching, so help them. The purpose of SEO is interpret what the search engines deem as signals of “quality” then to implement them the best way in the SEO campaign, presenting the site to Google in the best light possible. As Matt Cutts from Google said it, think of SEO as like polishing your resume’ , you’re not using tricks you’re just following best practices and sending the correct quality signals to Google.