I don't back up my physical files, no. As to whether it's necessary...I don't think so. As I see it, if all my physical papers went up in smoke, I could reconstruct what I need in a certain amount of time. I would spend far more time than that over the course of years backing up those papers (and storing them!), given the once-in-a-lifetime likelihood of that kind of situation.
I did lose my Hipster PDA once, and I reconstructed what I needed in about an hour. No problem.