venus - 11:30 am on Feb 6, 2008 (gmt 0)

Suppose I have a website with a home page PR-4...
and I go on creating new pages and add more content in it.

Is the Pr of the home page going to get decreased?
As far as I know, PR of a page is mainly determined by the no. of backlinks pointing to a page.
But at the same time some of my clients have experienced a bad fall in Pr during the last update....is it due to addition of new pages in the site? or something else?