Yes, you're totally cool to use either site.tld or www.site.tld. I'd recommend using a 301 redirect of one to the other (Google and Bing are pretty good at automatically canonicalizing these, but not perfect).
The trouble comes when you segment content to subdomain.site.com. The domain authority engines assign to a root domain may not always pass to all the subdomains, so you end up with subpar rankings to what you could earn.
As an example, we launched the Beginner's Guide to SEO on guides.seomoz.org and moved it after a few months to www.seomoz.org/beginners-guide-to-seo (where it currently lives). It had earned tons of links prior to that move, but the day after the 301 back to the main domain (away from the guides subdomain), it jumped to #1 rankings for all sorts of terms, including "seo guide" (recently got beat out by Google's SEO guide and is now #2). This was a good illustration of the power of keeping content in a single sub/root domain location for us.
> Google and Bing are pretty good at automatically canonicalizing these, but not perfect
I have been meaning to blog this - this leads to cloaking exploits. For eg. Google will figure out the shorter canonical link for a domain. So if you have www.lakers.com redirect to lakers.nba.com Google will treat 'lakers.com' as the canonical link and rewrite all the search results.
This can be exploited by registering a shorter domain and then pointing it to the real site, then waiting for Google to redirect it. For eg. Fred Wilson noticed that the guy who owns avc.com was redirecting to his blog. He thought the guy was being a good samaritan, until I pointed out that it was a cloak attack and he was trying to jack all of avc.blogs.com's Google juice.
You can avoid this by not letting Google or Bing setting the canonical and by specifying it with a rel='canonical' link or using Webmaster Tools. Do you know anything else about this Rand or have you seen it in the wild?
I talked to Fred about this after you pointed out, but there's basically no way that shorter url could have hijacked Fred's site. Way back in the mists of time we had things called "302 hijacks" but I haven't seen any attempts like that succeed in years.
Sorry, missed your reply. I was going to email you about Fred's blog but you were on holidays at the time, so I just asked him to setup the canonical in Webmaster Tools
one other thing why www is good for SEO. shitty URL parsers. lets say you make a press release. there is a high chance that www.example.org gets automatically parsed into a clickable link (sometimes it's nofollow, sometime it isn't) - on the other side, there is a high chance that example.org does not get parsed into a clickable link, so you would have to write http://example.org to make sure that it get parsed into a link, which is just ugly - and - most of the PR stuff are reluctant to do.
some URL parsers have caught up to non-www domains if you have a .com domain, but try it with an .io domain. it fails most of the time.
that means there are some interesting hipness tradeoffs
* if you have a cool .io domain
* you should have an uncool www
on other thing about non www domains. journalists always get it wrong: whatever you do, whoever you pitch, as soon as you end up in a big and might print newspaper (that also has a website) you will see your domain with www again.
Does anyone who is not a startup founders think kitschy foreign ccTLD domain names are cool? They just confuse users. I am waiting for the day the new Libyan government desides they don't want American companies exploiting .ly. That will be interesting to watch.
That's been my experience. Not only will the blog's pages rank better by being on the main domain, they'll also help the rest of the site's content rank better by bolstering that location's authority.
That said, I don't want to suggest this is always true all the time or that Google/Bing never group subdomain authorities together, just that we've seen inconsistency and thus I'd recommend keeping them together.
But if your blog is hosted by a third party (say Posterous), having blog.domain.com is very easy to set up, but domain.com/blog isn't? (Is it actually even possible at all?)
This is a total pain in Tumblr. I don't even think it's possible, or at least, haven't figured it out in 3 days of trying. So now I'm weighing whether the community/distribution of Tumblr is worth trading for a little bit of SEO. In our case, a social iPhone app, I think we're keeping Tumblr.
The trouble comes when you segment content to subdomain.site.com. The domain authority engines assign to a root domain may not always pass to all the subdomains, so you end up with subpar rankings to what you could earn.
As an example, we launched the Beginner's Guide to SEO on guides.seomoz.org and moved it after a few months to www.seomoz.org/beginners-guide-to-seo (where it currently lives). It had earned tons of links prior to that move, but the day after the 301 back to the main domain (away from the guides subdomain), it jumped to #1 rankings for all sorts of terms, including "seo guide" (recently got beat out by Google's SEO guide and is now #2). This was a good illustration of the power of keeping content in a single sub/root domain location for us.