I disagree. I have never had any sites get good SERPs without good PR. There is a correlation, but some people do overestimate the impact of that corellation.
PR has significance if you have a content site and in the scheme of things a high PR site/page will have a better / longer shelf life than one that has a lower PR. For example a churn and burn spamsence site that has no or low PR may rank well for several weeks but will fall by the wayside ... how do I know this ... have done many types of sites. Overall one way backlinks that are relevent will rise a site so the top.
I've seen PR help in my case when my site climbed a rank. I was no longer #2-3 on SERPs, I jumped to #1-2. PR is useful, in my opinion, when google is trying to decide between two (or more) sites for a specific spot in SERPs. If all other criteria are about the same, the higher PR may get ranked higher.
Google updates pagerank all the time, it's just the visual pagerank (the one you see in the toolbar) is updated about once every three months.