If you’re Matt Cutts and a billion people link to you because you’re the Spam guy at Google, writing great content is enough. For the rest of us in hypercompetitive markets, good content alone is not enough. There was nothing wrong with sculpting page rank to pages on your site that make you money as a means of boosting traffic to those pages. It’s not manipulating Google, there’s more than enough of that going on in the first page of results for most competitive keywords. Geez Matt, give the little guy a break!
Secondly, nofollow is also essential on links to off-topic pages, whether they’re internal or external to your site. You want to prevent search engines from misunderstanding what your pages are about. Linking relevant pages together reinforces your topic relevance. So to keep your topic silos clear, strategic use of the nofollow attribute can be applied when linking off-topic pages together.
The mathematics of PageRank are entirely general and apply to any graph or network in any domain. Thus, PageRank is now regularly used in bibliometrics, social and information network analysis, and for link prediction and recommendation. It's even used for systems analysis of road networks, as well as biology, chemistry, neuroscience, and physics.
Make it as easy as possible for users to go from general content to the more specific content they want on your site. Add navigation pages when it makes sense and effectively work these into your internal link structure. Make sure all of the pages on your site are reachable through links, and that they don't require an internal "search" functionality to be found. Link to related pages, where appropriate, to allow users to discover similar content. Denver Page Rank Click Here