This video from Matt Cutts about Pagerank is from August 2010 but is consistent with what Google are still saying today. Basically he says that it is the toolbar PR that Google is playing down, rather than PR itself. Toolbar PR is updated every few months and is just a snapshot of it at a given time. Actual PR is updated continuously. The reason for them playing it down is to encourage webmasters to think of all the other factors that are also involved rather than just focusing (as they have done historically) on what PR is displayed for their site: http://www.youtube.com/watch?v=h3Jup5R1MGY
PR does not matter any more apart from link exchange. But these days link building with irrelevant sites is a crime; Google thinks in that way. I think the popularity of PR falls straight away.
I've been watching and studying PageRank for years. I personally believe that PR is quite a bit less important now than it was some years ago.