The link attribute nofollow is used widely to control comment spam and not pass reputation or link juice to 3rd party sites. Strong opinions continue to be voiced about the use of the attribute on internal links within one's site.

The concept of using nofollow on internal links is to prevent bleeding PageRank to pages that are not useful in the index and don't contain content relating to your niche. Nofollow on a link on page1 to page2 prevents page2 being crawled and eliminates passing reputation, link juice, PageRank to that page.

Other Methods
The meta robots tag is available to nofollow all links on a page. The combination index, nofollow will allow the page to be indexed but all links on the page are nofollowed, while the noindex, nofollow combination prevents indexing and nofollows all links.

Robots.txt can be used to prevent indexing and crawling the page as well using the disallow directive. While this is acceptable for contact pages, privacy policies, etc don't use this to combat duplicate content pages. Why? If a page accumulates backlinks and is not indexed then it becomes a dangling page.

A better solution for duplicate content is to use the on page meta tag noindex, follow. This allows the page to be crawled and the juice to flow out of the page. Internal links pointing to duplicate content pages can be nofollow linked to minimize PageRank flow to those pages.

Strong Opinions
Like all things SEO, strong opinions in both directions have been voiced both advocating and warning against the use of nofollow links on internal pages.

I don't think the use of nofollow on internal links is particularly helpful for smaller sites. Those sites that have hundreds of thousands of pages with navigational links to contact pages can certainly benefit from the granular use of the nofollow attribute on single links.

For blogs with duplicate content issues that are not resolvable with a plugin and site design, it is a necessity to prevent link juice leakage.

For those that warn that Google will ban you, penalize you, de-index you, and take you off their Christmas list for using nofollow on internal links read what Matt Cutts said in Google groups on October 8,2007.

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