Anyway, I guess you were expecting one of those hokey quizzes news sites have that never really cover the bases properly. shrug PV's actual purpose is to enhance constituent communications. That means your messages to Congress route through them so they can sprinkle on loads of metadata and make it easier for the Congressional aids to sort through while at the same time providing public accountability. This personalized bill-by-bill member-by-member thing is newly added on top of that larger main goal.

I use it because I like that accountability thing (transparency, woo!), and I have enough friends that used to have to sort through paper letters to the offices they worked in who have warned me that I will make staffers hate me if I send paper letters ;)