I do it on my iMac all the time.

Power: i would hope so

Mini-DVI: connected to 18"CRT

Ethernet: wired to PowerMac G4 for uber fast transfers

Firewire 800: don't have anything to use it yet...

Firewire 400: wired to PowerBook G3 to grab some files

USB port 1: keyboard because it needs the power for the ports

USB port 2: 4-port usb hub

USB port 3: iPod

Sound in: refuse to use this because it generates so much noise

Sound out: wired with a headphone splitter that splits the signals to my Pioneer stereo and a set of computer speakers by my bed.