PVC is the most expensive pipe to use for shop air! I used to work at a shop that used it and while I was there saw a customer run over an air hose and the quick coupler on the air hose tore the skin on the door of a Mercedes CL600 and nicked the rear quarter panel. I think the repair was around 9K! I have also heard of mechanics just stepping on an air hose and breaking the pipes.
In my garage I am using copper with all of my air drops off set with drains controlled by ball valves at every drop.
http://gallery.bcwolff.com/default.aspx?moid=12434
I also have the garage split up into sections with ball valves and unions to allow me to cut off a section of the system for changes or repairs. The copper is pretty cheap and very fast to install with just a cutter, torch, soldier and flux.
My goal on the system was to be able to work in any area of my garage without having to stretch a hose across a car.