My Business Puter is always on, goes to a screensaver. Media computer is on 24/7 with movies streaming. My DAW with Digi 001 and Pro Tools 6.4 (a dinosaur) is always on, so I don't have to wait to jump on it and start mixing. But that one cannot hibernate, the Digi hardware prevents it from going into hibernation. There is a PCI card that connects the 001 module. All three of these systems connect to a 40" Hitachi HDTV as a display.
On the other side, my work area, I have a mac G5 Titanium Tower, always on. I had hoped to run Virtual PC, but it is very slow. Since it's 10.5.8 for powerPC I can't do Boot Camp. It has a 21" Cinematic Display that is beautiful. Speedwise it is comparable to an Athlon socket 751, it's got 3 GB of ram. That one goes to sleep. Sometimes I have other systems hooked up there, that I'm working on, those stay on as well while I have them.