PageRank (PR) is a calculated metric that part of a much larger part of the algorithm which deals with Popularity (note: the other two large areas of the algo are: Content & Architecture).
PR in itself is not the end all of rankings … as you can see from some of the replies above, PR doesn’t guarantee anything, but as much as I hate to admit it – it is a part of the algo – just as LocalRank and all the other sub-algos that look at link equity.
The other part is Toolbar PR is simply an average estimate of the true value of PageRank. I like to tell people that the TBPR is there simply to mess/confuse the minds of webmasters as they concentrate on it all the time. The PR displayed in the Toolbar updates a few+ times a year and is a metric to look at, but that is about it.
If you sit there and base all your decisions & strategy on it, you will probably get more and more confused.
Just sayin …