In a recent interview with Priyank Garg, Director of product management for Yahoo! Search Technology, conducted by Eric Enge, we were told that Yahoo breaks pages down into template sections to distinquish between noisy, or boilerplate content, and unique content:
One of the things Yahoo! has done is look for template structures inside sites so that we can recognize the boiler plate pages and understand what they are doing. And as you can expect, a boiler plate page like a contact us or an about us is not going to be getting a lot of anchor text from the Web and outside of your site. So there is natural targeting of links to your useful content.
We are also performing detection of templates within your site and the feeling is that that information can help us better recognize valuable links to users. We do that algorithmically, but one of the things we did last year around this time is we launched the robots-NoContent tag, which is a tool that webmasters can use to identify parts of their site that are actually not unique content for that page or that may not be relevant for the indexing of the page.
If you have ads on a page, or if you have navigation that’s common to the whole site, you could take more control over our efforts to recognize templates by marking those sections with the robots-NoContent tag. That will be a clear indicator to us that as the webmaster who knows this content, you are telling us this part of the page is not the unique main content of this page and don’t recall this page for those terms.