This is a video that I presented for work, helping people to better understand where the most valuable places to put a keyword are in a document, or blog post.
It really is true that there are those three main areas that you will want to make sure that your keywords are in. You don’t want to overdo it though. There recently was a talk from Matt Cutts talking about people who will over optimize their keywords within their content. He said that they are working on a chance within their algorithm which will devalue sites that are over optimized that have a keyword put into everything way too much. Or just have a lot of work done to it in a very short amount of time. So you want to be sure that when you are optimizing your site that you play it smart and be sure to put it within the areas it needs to be, and not over do it.
Of course if there are any questions or things you are curious about this for sure let me know. I will see if i can find an excerpt from where Matt is talking about this change, and put it here in this post.