Why would you care about PR? It means nothing to anybody other than those who are in the business of buying and selling PR links.
As per my knowledge PR is a small part which will help your site to rank. The links and the content is the major thing for any site to rank and if you have good links PR will grow automatically.
The PR that people moan on about doesn't exist though. Google has an internal algorithm for calculating "PR" which isn't revealed publicly. The PR we all see on a bunch of toolbars is worth absolutely nothing - unless you're selling PR links to blind fools who also buy in to the myth.
Collect quality backlinks from doing some off-page optimization. It will help to get good pr but remember that laways submit your site to niche category...