i could do with a few opinions please on the following. I own a domain which is 5 years old has 100s of pages in google and is a PR4. We want to launch a couple of new areas to the business and wondering do we a) use folders for them so it's domain.com/newfoldername/pagename.php (i need to use the folder name bit as each of the sections will have it's own index page etc) or b) do we set up subdomain.domain.com allowing one sub domain for each of the new sections? Whilst subdomains are looking appealling in terms of making the site nice and tidy doesn't Google consider them to be new domains and so they will have to build up their own links, age and trust before Google ranks them, whereas with using the sub folders they are placed on a domain with years of age and 100s of backlinks and whilst little pr will be passed to the new pages the trust and age value of the domain should be? does this thinking hold correct? thanks
Subdomains are treated as separate websites by Google. So you are correct that they will have to get their own PR and trust. The way I decide is by "major theme". If the new topic is completely different I make it a subdomain because it is easier to get a new theme to rank in google when it's on its own domain. If it gets mixed in with your other site it may dumb down the theme of your site and thus reduce your rankings. Bottom line. Same theme same site. Different theme different site.
Sub-domains can still be juiced from your main domain web pages for Pagerank since they still sit on the same domain name, trust will not be a factor as well. As to the question on hand, you should just use sub-folders. I don't recommend using sub-domains unless the content is not directly related to the main domains content.