Here's an article that details some statistics on the averages of keyword saturation within the top 3 SEs. The numbers are interesting, and the article well thought-out. I just wonder if the mantra that I've been hearing, "Create quality content for your users" usurps the need to worry so much about having a keyword in an article an extra time or two.

I found this article stressing the importance of being ranked #1 in Google for your particular keyword. It has a "chart" that shows the rough percentages of clicks that will typically be made for the ranks on the first page of search engine results.