Subdomains & URL structures for large site

[webrankings]

I am building / project managing the build of a large website.

The site will have social networking, forums, blogs, a shop and articles, videos and information.

What are the pro's and cons of subdomains.

I know people say that each site will be a stand alone site in the search engines eyes. However when moving around the site it will be fluid between subdomains and there will be a large number of links between.

My main concern is that my plan is to market the free aspects of the site and that the shop will gain on the back of it. So I need the shop to rank.

My thoughts were:
forum.xx.com
blogs.xx.com
shop.xx.com or xx.com/shop (however this extra slash is not good for seo purposes?).

Any help would be great.

[tedster]

This question seems to come up every few months, year after year. For example: this discussion from last December [webmasterworld.com].

Whether you choose a different hostname (subdomain) or a subdirectory should mostly be up to your maintenance needs, I'd say. I usually prefer directories because that approach has not been subject to algo changes the way hostnames have been.

[BradleyT]

Directories.

[webrankings]

For good reason. It may come up every few months but since there is not a clear cut answer (there were disagreements in the thread posted plus talk of future change) I still think it's a valid question four months later.

Also I am seeing a results page for a highly competitive phrase with three subdomains of the same site being scattered across the page.

Thanks for the response though.

I like the idea of different sections of the site having different rankings plus it should make it tidier. - sub domains.