Here's a video of Strobeshnik, a pretty impressive HDD clock mod, you can check out the project over here.
Strobeshnik is a HDD clock. The digits are etched in the original platter and they're strobed from behind with leds. The HDD motor is driven by a custom circuit without feedback, hence poor startup performance and awful noise. Rotational feedback is provided by an IR LED/phototransistor pair near the place where the head arm formerly was.