Was helping someone with their computer and related problems tonight, moved an x86 PC from one side of the room to the other. After plugging it into the wall, and pushing the power switch there was a moment of silence, during which I started to turn the machine so I could make sure I had flicked the power switch on. A moment later the sound of a gunshot rang out and smoke started pouring from the power supply. After making a safety run outside with the machine and pulling the parts in question I dismantled them.
A small electrolytic capacitor on the power supply board had decided to overheat and fired its casing off like a rocket, which left the insides burning till they were gone. This was the best computer failure I've had to date, personally.