Well, I've used 1/2 I.D. PCV pipe on my compressor and 2 of my buddies garages... now keep in mind, these are not a professional shop... they're just home garage setups... The line goes up from the compressor, along the ceiling, drops down a post to the water trap and back up the the hose reel. It's been years without incident... the pipe is rated for 600 PSI.
Having said that, yes copper lines would be better without a doubt or the new nylon tubing designed for compressor lines which is what I plan to update with soon... (See attachment)
Below is link for US Dept of Labor document on the use of PCV pipe on compressed air or gas lines...
http://www.osha.gov/dts/hib/hib_data/hib19880520.html