i haven't check my site PR for the past 1 year because PR is useless... it doesn't have any effect...
pr is based (from what I understand) on the amount/quality of your back-links. If you concentrate on getting good links to your site your pr should increase.
I think PR is just for show. I've seen a lot of websites with a PR of 0 but they're number one in Google.
Current ranking in Google depends on the actual PageRank value (constantly updated and internal to Google). The toolbar PR value is usually really, really out of date, possibly a year or more. The toolbar PR won't tell you anything about where a site would rank today.