The website I am actively developing went from PR 3 to PR 2.
andddddddddddddddddddddddd
Another domain I own, but never developed – that has had two banners and a “coming soon” paragraph on it for 6 months -went from PR 1 to PR 3!!!
Way to go Gooooooogle!!!!
PR is largely an indication of the logical/illogical flow of your site navigation system along with incoming links. Little more than that, but it is still useful. A small site with 1 page is as likely to get a PR 3 as a site with 1,000 pages. If your PR is sliding, then it’s time to analyse how your internal page links work. Similarly a site with 1,000 incoming links and illogical/poor in-site navigation may only get a PR3 also.
Low PR may mean bad linking, orphan pages, lots of pages in a site but only one link to them internally, heavy weighting of incoming links to one particular page etc etc etc. And PR filters in and out also don’t forget. Just use it as a general feel as to how Google thinks your navigation works for users and change accordingly.