I saved an old NetApp FAS960 faceplate from the e-waste pile. There's an arduino glued into the back, and LEDs run to the original spots on the filer's grill. I added a photo resistor on the top left corner -- so waving your hand over it causes a measurable drop in light level, letting it be a sort of gestural input. (Sort of.)
The initial application was as a timer for backup tape acclimation. When you bring new tapes into the datacenter, you'd wave over the photo resistor, resetting the clock, and then in two hours it'll illuminate the blue LED, and in six hours it does the green LED ... indicating that the tapes are adjusted to the datacenter environment. That works fine, but I'm still not sure what it wants to be when it grows up.