I would say we should not be concerned about
PR update instead thinking of ways to add content benefiting the audiences. I am setting up sites that I want people to visit or buy my products / services so I would put my concentration to improve the content / products / services so I will get more visitors. I do believe if you add quality contents, it will eventually help you to improve ranking as well as sales.
Bottom line, we want quality and targetted traffic to our sites and not concerning too much about
PR updating. This is my personal opinion.