PHL and EWR (along with CDG) are the three airports that are some of the worst to sleep in (well HNL actually closes the airport and tosses everyone out).
There are quite a few homeless in PHL, EWR and CDG and the cops don't seem to do much about it. These are three of the airports I will never sleep in (I seem to regularly sleep in SFO and LHR no problem, castles compared to PHL which is more like a dungeon.