martinibuster - 4:00 am on Sep 18, 2012 (gmt 0)

The h1 should be the primary keyword phrase...

Yes and no. The issue of keywords had been updated. More and more Google is dealing with concepts in order to bring up a wider variety of candidates for the top ten in order to select the best answer for a query. It's not always necessary for keywords to be hammered on the page.

The header tags should be thought of as a way to provide an outline of what the entire web page is about. The analogy of a pyramid is quite appropriate. A reading of The Elements of Style [bartleby.com] by Strunk and White is recommended to obtain an understanding of the concept of ordering thoughts on a page to form a coherent document.

The W3C has a tool [validator.w3.org] that displays the "outline" of a web page. Basically it grabs your headers and creates an outline of it. A poorly created web page will be diffuse while a well thought out web page will create a scannable outline of what the page is about. This is the O part of SEO, optimization, that gets forgotten, which means making it easy for the search engines to understand what the web page is about.