Hey, Digg.com team! Are you aware that your domain names aren’t properly canonized? You may be losing out on good ranking value in Google and Yahoo because of this!
Even if you’re not part of the Digg technical team, this same sort of scenario could be affecting your site’s rankings. This aspect of SEO is pretty simple to address, so don’t ignore it and miss out on PageRank that should be yours. Read on for a simple explanation.
Top search engines use the number and quality of links to a page to define its popularity/importance. If you have two alternate URLs for the same page, and they both get indexed, the search engines don’t automatically combine the rank for the separate URLs into one. Ex:
Simply put, search engine algorithms may treat those two URLs as though they’re two different pages. One might have three external site pages linking to it, and the other might have two linking to it. A search engine would not assess the page as having five inbound links, resulting in the page getting less linkweight and associated rank attributed to it.
What many people don’t realize is that alternate domain names can have the very same effect, and negatively impact a site’s rankings even more significantly.
I was posting tonight about tips for gaining popularity in Digg, and I was going to their site a few times over to check out what sorts of links were presented on their top pages when I glanced up at my Google toolbar and realized they had zero pagerank! That situation was so unbelievable for such a popular Web 2.0 site that I did a double-take. I then realized what happened.
I had typed in www.digg.com, which is apparently their less-preferred domain name version. They’ve apparently trained their users to predominantly use digg.com without the “www” prefix. Digg.com with the www has zero pagerank. Digg.com without the www has a PR of 7.
Now, if they’d trained everyone on earth to use their preferred domain name in links, this wouldn’t be a big deal. Unfortunately, they didn’t. You can see 642,000 pages indexed in Google  for that nonpreferred domain at the moment, and 187,008 in Yahoo! .
What Digg’s team and many others don’t know is that this situation of not having all your domain names resolve to one primary name is called a canonization problem. One primary name needs to be made canonical for their site, so that all their PageRank can be merged and attributed to one single domain. Having all their PR gathered together on one domain instead of divided onto two could actually help them get better rankings in the major search engines, along with the attendant traffic that could go with that.This is so easy to fix! In Google’s case, Google actually allows you to instruct them to group the two domains together via their Webmaster Tools, Sitemaps section (description here ). A better solution IMHO is to set up 301 redirects on your server, redirecting all queries for the www url to the url without.
I think this is a better solution, since it sends the SEs a clear signal as to what the preferred domain should be, and this approach works with all major engines.
Oh, I may as well let you Digg This  if you want to!