All PR is totally useless unless you are just using it to get money but other than money PR doesn't matter.
PR is basically important if you plan to sell links. It does show a rating based on the quality and quantity of your back links. Until you reach at least PR3 or better, it does nothing for your ability to sell links.
For purpose of selling text links, anything under PR3 is totally useless. For search engine rankings, even PR0 doesn't matter.
PR Rating is useful only for robot traffic. What is important is real human visitors and traffics because that is what really counts. Sites can have PR0 and yet be very successful because it draws in the crowd. Some sites with PR5 may have little to no human traffic if all it is used for is to get backlinks through internal linking.
PR is nothing. As long as your site has good content people will love your site. Once people start liking your site you will get natural links from people linking to you, which again contribute to increase in PR.
PR that is <= 5 is fairly easy to achieve if you have a content site. Moving up after that is a lot more difficult.