Query / Discussion on Subdomain and Root domain passing authority etc

[James77]

I've seen Rands video on subdomains and best pratices at
http://www.seomoz.org/blog/whiteboard-friday-the-microsite-mistake
http://www.seomoz.org/blog/understanding-root-domains-subdomains-vs-subfolders-microsites

I have a question/theory though and it is related to an issue I am having.

We have built our website, and now we are looking at adding 3rd party forums and blogs etc (all part of one CMS).

The problem is these need to to be on a seperate subdomain to work correctly (I won't go into the specific IT details but this is what I have been advised by my IT guru's).

So I can have something like:
http://cms.mysite.com/forum/

Obviously after reading Rands post and other stuff this is far from ideal.

However I have another Idea - run the CMS from root and the main website from the www. subdomain.

EG
www.mysite.com
mysite.com/blog

Now my theory is that because so many website (possibly the majority - especially smaller sites) don't use 301 redirects between root and www. that search engines may make an exception in this case and treat them both as the same domain, so it could possibly be a way of getting round the issue.

This is just a theory of mine, based solely on my thoughts that there are so many websites out there that don't 301 root to www. or vice versa, that possibly it would be in the SE's self interest to make an exception and count these as one domain, not 2.

What are your thoughts on this and has there been any tests done to see if this is the case or not?

Thanks

[MichaelC-15022]

I'm pretty sure this won't work....Google will still treat those as separate domains.

What I saw 2 years ago was pretty compelling evidence that ZERO domain authority was transferred between subdomains.  More recently, I've seen examples where it seems that this has changed a little, and SOME of the domain authority was carried over....not sure how much, but the examples I saw made it seem like it'd be in the 10% to 40% range.

Now, let me throw out a suggestion your IT folks might not have thought of:  you may be able to appear to host all your content on your www subdomain, even if the content itself is physically hosted on separate servers.  All that's required, really, is that the main domain's servers implement reverse proxy for the other domains.

Slingshot SEO posted this article on reverse proxies a while back, and it's definitely worth a look.