I was being facietous, of course. I hope Ron Doran will chime in here, because his opinions are well rooted in both code and practice. I can only speak on experience because I don't have a background in the electrical trades.
I have experienced many installations in which 120 VAC and the output from a 480VAC variable frequency drive were run for a moderate distance (100+ feet) in the same conduit. We got a lot of induced noise on the PLC inputs from those 120VAC input points, causing false input signals. This is far less likely with "clean" 480VAC, but the longer the conduit the more likely that induced voltage will be a problem.
"Code-wise", I have only experienced problems when users get their hands on 300V insulated appliance wire. Typical "THHN" wiring that I see used in industrial applications has 600V insulation and can be installed in proximity to equally insulated conductors that are carrying 480VAC.