Press releases and directories don't amount to shit anymore on any decent keywords.
BTW, just for all the people contributing their sparkling gems of digitalpointesque ignorance: blog commenting is a way to build backlinks, but blog comments in and of themselves don't get you further up the SERPs.
PR has everything do with SERP, because PR is a mesure of the quality (relevance, authority etc) and quantity of your backlinks. Saying that PR has nothing to do with SERPs is like saying GDP has nothing to do with a country's economy.
As mentioned already by someone who does know what they're talking about: the PR in your toolbar (and in all the checkers) is the external PR, out of date, inaccurate. Google updates your internal PR every time it notices a change in one of the elements that factor in its PR calculation (backlinks are the most well known factor, there are others). Google pushes out their internal PR every 3 months or so (the infamous PR updates) but it has no effect on the SERPs because they've already been using their up to date internal PR.