Backlinks are the most effective way to get high PR but you can't neglect other promotional activity for getting good PR for the website like - content on webpages, inter-linking, anchoring, domain age, website's market, etc.
fromthe5 and about 1/2 of you are absolutely right. PR is all about authority, authority is based on how many pages (outside of your domain) that point to your page. So, PR can't be increased by content value, it's impossible. You can have a crappy page but if you have 100,000 links pointing to it, guess what, HUGE PR. I'm not saying it's right, I'm just stating facts.
The reverse happens all the time. Haven't you ever gone to a great site with a ton of traffic and a PR1 or even a 0? The window for this closes quickly as word spreads and backlinks climb.