Permalinks and SEO in 2011

Expert Feedback on Best Permalink Structure for SEO in 2011

 
Amazon and eBay are just two websites that have modified their URL structures over the last several years, parsing out categories and subdirectories from permalinks. The trend seems to be picking up, though it somewhat goes against traditional SEO siloing and taxonomy best practices.

This survey is designed to help build a current business rule for permalink structure through use of case study, experience, and expert opinion.

This survey will end on June 1st, 2011. Results will be posted for review and discussion at http://www.seosteve.com/ by June 5th, 2011.

Please share this survey with other experts in search engine optimization to help us draw a more conclusive answer. Thank you for your time and participation.
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Ignoring for a moment www prefix, file extensions and trailing slashes, please select the sample permalink structure that you believe is best aligned with current search engine optimization best practices.
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Matt Cutts made it clear in a 2010 video that file extensions help Google determine the document type. However, more and more websites are removing file extensions to shorten URLs and to match AdWords display URLs (when the same page is being used for SEO and PPC).

From an SEO perspective, which way do you lean in general toward file extensions such as .html, .htm, .asp, etc.?
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Having a www prefix has been said to be better than not having a www prefix, based on how users typically "blind link" to content (without copying the URL from a browser address bar), despite the fact that Google Webmaster Tools allows you to choose either www or no www.

Example: http://www.Google.com versus http://Google.com

In your experience, what is better for SEO, prefix or no-prefix?
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Forced trailing slashes at the end of URLs (file names) that do NOT include a file name extension (.html, .htm, etc) have been said to improve SEO, reducing duplicate content and encouraging more efficient backlinks from visitors.

Example: http://www.google.com/keyword-themed-page/

On the other side of the fence, PPC advertisers who don't use standalone landing pages for paid search may argue that no trailing slash improves both paid and natural search.

Where do you stand as a general rule of thumb?
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Capitalization of words used within URLs is another important permalink topic. Please select the structure you believe is the best from an SEO perspective (in general).

For this answer, please do NOT take into account file extensions, www prefix, directory structure or trailing slashes.
If your answers were based on research you performed online, please use the box below to paste in the URLs to the supportive web addresses so that we can include them in our study. This isn't a quiz, it's a study, so all supportive articles and case studies are appreciated.
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