I think Permissions are the most messed up part of OS X, but device management on a multi-user machine is a close second.
Specifically, management of owned devices.
So a drive that's shared between all users seems to work. CDs can get stuck though. They become invisible except by using Disk Utility to force an eject (sometimes the hardware eject button will work).
The real problem shows up with iPods however, and presumably with an iPhone as well.
Each user account tries to seize control of the iPod. So if I sync on my account, then switch to my wife's account, the iPod can go into a limbo state. It thinks it's attached, but the OS says it isn't.
It's almost as if Apple doesn't really support use of an iPod on a multi-user machine.
No, that couldn't be ...