It is my understanding that in relation to Google, subdomains are treated as a separate domain, whereas a /folder would be counted as the same as the parent domain. Hope that helps. I guess it depends upon what you hope to accomplish.

If you wish to have the parent domain garner the most links/juice the quickest, then perhaps the /folder model would be best. If the topics are not coherent and relate, then perhaps the subdomains would be best.

I am a newbie, more or less a month into blogging. I used a subdomain for my other interest. When I checked PR, the main is still zero but the subdomain is at 1.

Advantages as to what? SEO? Usability? Scaling?

For SEO, the sub may be treated as another site, but I believe Google has done some things in this area, due to many sites using it as a SEO trick.

For usability, it depends on the content.

If the content is completely unrelated and you don't want to use another domain, a sub can be the right move (like about.com).

However, content that's simply an extension of the site should be put into folders (widgets --> blue widgets --> green widgets, etc).