As a Webdesigner I recommend you to watch out to not exaggerate with using the keyword in your texts. This will destroy all effort for usability, and people won#t trust your information if it looses its natural feeling of language. This is my opinion.
On my pages (e.g. http://www.schnellkochtopf-tester.de - it#s in German) I try to stick with a density of max. 10%, which already sometimes feels to dense.

2-4% keyword density

Keyword density is the percentage of times a keyword or phrase appears on a web page compared to the total number of words on the page. In the context of search engine optimization, keyword density can be used to determine whether a web page is relevant to a specified keyword or keyword phrase.

Keyword density is the percentage of times a keyword or phrase appears on a web page compared to the total number of words on the page. In the context of search engine optimization, keyword density can be used to determine whether a web page is relevant to a specified keyword or keyword phrase.

Keyword density is the proportion of times a keyword or word seems on an internet web page in comparison to the total range of words at the page. Inside the context of search engine optimization, key-word density can be used to determine whether or not a web page is relevant to a particular keyword or key-word phrase.

Keyword density tells you how often a search term appears in a text in relation to the total number of words it contains. For example: if a keyword appears three times in a 100 word text the keyword density would be 3%. From the point of view of search engines, a high keyword density is a good indicator of search engine spam.