I also have a PR0 site ranking #1 for at least 10 Highly competitive keywords...
Years ago when Google first appeared Page Rank carried MUCH more weight in Google's rankings than it does today. It's what made Google different at the time. The PR of URL X today, however, is only a miniscule factor in how URL X ranks for a particular keyword phrase. It's not even worth thinking about. PR0 pages outrank PR8 pages ALL day at Google...
Google is now all about relevance... is the content found at URL X relevant to the user's search phrase, how many inbound links to URL X contain keywords relevant to the user's search phrase, are the pages linking to URL X relevant to the user's search, do the inbound links to the pages linking to URL X contain keywords relevant to the user's search, etc. These things affect many ranking factors at Google.
Page Rank is a measure of link popularity - # of links and strength of those links (whether the pages linking to your URL are also popular or linked to). The formula has absolutely nothing in it related to relevancy.
Google has changed over time. The only people still hanging on to the myth that if they have a PR9 page that it should rank decently well for any query out there are those selling links. "Buy a link on my PR6 page for $200/month and you're sure to increase your rankings." If that page is not related to my topic, I can get just as much boost to my rankings by getting a link on a PR0 or PR1 page that IS relevant.
The PR of the page BEING ranked is not that important. Having links from high PR pages that are irrelevant to the topic of your URL and that use link text that are irrelevant to the topic of your URL (for example, "Click Here" as link text) does NOTHING noticable to your rankings. Yea... you get a little PR for your URL but the PR of the URL being ranked is likely some small percentage of 1 percent of your overall ranking score for a particular keyword.
If however you have inbound links with relevant keywords in the link text then if the page linking to you (not YOUR URL) has a high PR then that will make that link even stronger. But the PR of the URL being ranked is insignificant now days.
And, of course, the PageRank that a page really has and the PageRank that Google displays to the toolbar are often not the same.
Sometimes this is because toolbar pagerank (TBPR) is slow at updating, other times it is because of a TBPR penalty.