If you don't use your capslock/numlock/scrolllock on your keyboard you can use those LEDs to indicate hdd, network or even cpu activity (kernel must support it) by writing the appropriate command to the sys interface like this
echo "disk-activity" | sudo tee /sys/class/leds/<your LED>/trigger
supercool thanks!
IIRC, BeBoxes had two strips of LEDs on the front that indicated processor utilization. They should bring that back.
Does your motherboard have a parallel port header? Connecting some LEDs is trivial. Writing a short C program to display CPU utilization on LTP is not that hard either. There goes your weekend.
Also continuous or intermittent audio status indicators.