Article marketers generally understand that keyword stuffing results in content being penalized by Google, and will try to include keywords naturally and a reasonable number of times within the text. When I'm writing an article I use the main keyword in the first paragraph and again in the final paragraph. How many times it appears in the middle section depends on article length and the number of other keywords used in the same piece. I've been told that placing keywords at the start and finish is effective for SEO. If it's true, I would be interested to know why, and I wonder how many article writers make the effort to do this.