consider your domain is testdomain.com if someone links to testdomain.com/blog or /something, will it add PR only the /blog page or also to the root one? I hope that was clear.
It would add only to the subpage, i suppose. Page rank means rank of the single page so it counts to only the page which is linked.
i am agree with chetan.most of the inner links point to home page than your home page PR will increase.
PR is a function of IBL's (in bound links) Everytime a different link points to a page, it passes a portion of the PR from the page on which it resides, to the target page. Dave
It adds PR to the page that is linked to. Though PR is then transferred to other pages on the site through your internal link structure.