Many sites throughout the web could be picking up more long tail traffic by varying their navigation. Based on what I’ve seen, by having the same primary navigation, secondary navigation, header, footer, and sidebar on each page, you are significantly diluting the relevancy of each page.
I’m working on a client’s site as we speak which as about 85% of the same content on each page (nav elements, header, footer, two widgets, sidebar, etc.) and if you use the Google Adwords Keyword Tool I can tell that Google thinks most of the pages are about the same keyword set, even though that is not the intention of the webmaster. When 85% of the source code is the same on each page, it’s easy to see why Google may think this. This is something that needs to be discussed as the site is being developed. Unfortunately this is not always the case as not everybody designs their site with SEO in mind.
What are some ways around this? One method would be using iframes on the footer or header so that the contents of those pages are only indexed on the actual frame page and not every page. I feel iframes have a negative stigma attached to them as they could do lots of harm if not used properly, but they are a good option for boiler plate content. You could also not feature the footer on every page.
The best solution, although hardly the most practical (especially when dealing with clients) would be to redo the navigation. Have clear primary navigation with a few links that appear on every page, but make sure the secondardy navigation is based on where you are on the site and make sure to have breadcrumb navigation. The more unique content on a page will make it easier for the search engines to figure out what a given page is about and how it fits into the hierarchy of the rest of the site.