For several years now, good sources at Google (like Matt Cutts) have indicated that keyword density carries little or no importance in their algorithm. Keyword related factors that are still considered include anchor text for editorial links, page title, page url, and heading tags. They also seem to reward pages with lengthier content, maybe 500+ words, and long tail keyword variations.

Check your copy and eliminate: it -- it's -- that -- those -- they -- them, etc.

Therein lie opportunities to further clarify what you're writing about. Of course, proceed with caution and be sure, above all, your writing doesn't feel forced.

Hope that helps!

Its not the number of times but a percentage of total words on the page. I've been told 8 % is optimal.

The best approach is to write valuable content for your visitor, this in turn puts relevant words and phrases that form your keywords:

1. in the write place: above the fold for the visitor = top of the text flow for the search engine (in most HTML pages) which tells the search engines that the words in question are what the page is about.
2. and with the right density: unnecessary repetitions confuse and bore visitors = high density of keywords hurts your credibility with the search engines.

This is NOT to say that at any given point of time there is no specific formula for keyword density. However if you somehow determine and comply with this number now, there is almost a guarantee that you will be out of compliance at some point in the next year or two, forcing you to re-organize or even re-write your content. So, write for the visitor, keep your keywords in mind when doing so, and devise your HTML text flow accordingly.

And finally yet most importantly, pay a lot of attention to your internal and external links and the anchor text for them, as the anchor text of a link leading to a particular URL is similar to the business card of a businessperson: a small but powerful aid in forming a first impression that can be bolstered by what one sees when one gets to meet the business person which is analogous to reading the content on a web page.

Earlier it was said that a page should have at least 30% density but now its around 10 to 20%