Totally agreed. Google PR was once a useful indicators for website quality - but not after every webmaster knew (and manupulate) about it. Back to the question... seful content can be helpful indirectly for building up PR, indirectly - especially your contents are link baiting or and attracts discussion from other websites/blogs. However, if you wanna push the green bar up fast, buying links from other high PR website is the best way to go.