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With directories it's all about getting links and anchor text. Will links harm a site? Never, if they have some quality. If you like the quality of directories i think you should go for it.

I agree, Google offer a great search experience to users. If by having a great product you can achieve 80% of the market share in a territory you undoubtedly need to ask is this good for consumers?

John - Thanks, i'll start here. I'm not sure why they are set up like this (facepalm)

I agree with Steven on everything he said. Google has been putting a lot of emphasis on making sure SEO's are utilizing GWT as a resource for usability and correct data.  I'd use that as your primary source.

hmm, I actually need a near to complete list if possible

Ensure you have unique and contextually relevant content ( text, images, video, audio) exposed on the dynamic page. As I understand it the engines are looking for content which has a valuable user experience. In the case of Google and Bing they are using their respective toolbars (and analytics services) to measure user engagement signals. In this case, quality and maintaining rank for pages is reliant on both the content and user acceptance of your content. Ask yourself a simply question, will this page satisfy any user who comes to it? I try and have a question and answer for each page on my site, if the page content does not answer the question then I think again about how I can best deal with solving that.

I say Test it. Buy a 2 and 4/5 word domain for the same vertical and see which one ranks better faster.

As Ryan said, do 301's. You don't want to have the old versions up and canonical them if you don't have to. Imagine the confusing surfers that land on something because of an old link, and then click around and end up on the new version.

Duplicate links on a page are fine. As EGOL shared, you only want to offer a duplicate link when it makes sense and offers a benefit to users. The SEO community all seems to agree only the first link is counted with respect to Google, but I have been unable to locate an authority such as Matt Cutts who provides a response confirming this information.

301 one of the domains to the other domain. That should work. You need to decide if you want a www.site.com or a non-www, just site.com. Keep it consistent from here on out. Code for htaccess to redirect non-www to www: RewriteEngine On RewriteCond %{HTTP_HOST} !^www.site.com RewriteRule (.*) http://www.site.com/$1 [R=301,L]

You could also potentially offer RSS feeds for many different categories of products: newest products, top sellers, screaming deals, get-it-while-it-lasts, etc. Since RSS feeds are useful for deep indexing on an eCommerce site, they are valuable for both consumers and bots alike.

Thanks.