I dislike PFF, I don't like their numbers and I don't think that their analysis is very well done. Ask yourselves this, why are they not applying this type of widespread analysis to the college game where if this analysis was as good as they claim it is then they should have no trouble picking out and finding legitimate prospects (noticed they have started by doing one game a week I believe).
Having said that there are not many or any objective analysis of players in the NFL so while I think their analysis is flawed it is interesting to see how the league compares on their 'objective' scale, but anything written by PFF should be taken with a huge grain of salt.