SubDomain vs. SubFolder

[tdawson09]

I know this subject has been discussed many, many times before. But it is now 2013, and Google continues to tweak and change their algo to build upon the best delivered results for users.

So the questions are:

Does Google still treat subdomains as a completely separate and unique domain from the root?

If so, is it a good SEO strategy to split up, when it fits, a website into subdomains with links pointing back to the root or main domain?

As a company we have several subdomains with some of our categories. For example our main site is www.iboats.com. This site has all our boat products. But we set up subdomains several years ago for the following:

boatcovers.iboats.com

boatpropellers.iboats.com

biminitops.iboats.com

And we have our fourms as a subdomain: forums.iboats.com

Splitting them out were originally done for SEO reasons, but now is more for better managing our main categories.

It appears that Google is treating our subdomains as part of our main root domain anyway, so I don't see the SEO value anymore. If we were to move the subdomains into subfolders of the root, I'm wondering if we might see a boost in SEO value having more pages within the main website?

I'd be interested in everyone's thoughts on this subject.

[tdawson09]

Are there no opinions on this topic?