[CycloneFE]

I have done some "googling" and found a lot more. Plastic and PVC probably just fine for average air stuff, but if you want to really move some air for some heavy tools or blasting, the required PSI may cause failure in the plastic. The iron pipe has been warned of rust, but isn't that what you have drain valves for? Copper has a major cost factor, and I know as I have just finished putting my plumbing in using copper.

I guess the air line looks like a nice early summer project. Feel free to add any more ideas or situations you have, I like listening to people who really do this sort of thing.