My experience says that PR doesn’t matter much. Maybe the difference between a PR1 and PR2 means something since it doesn’t take many backlinks to achieve a PR1, but then requires exponentially more backlinks for each level of PR.
Our site was a PR4 a couple of years ago, but has settled into a PR2 for the last 12-18 months. In the same time span, our search positions have only improved. We even have PR0 pages showing in the first page of results for competitive keywords, so no I don’t think PR is all that important.
PR is really only important to other webmasters who only consider PR when buying or exchanging links.