No electrical fires here, but my PIII-850 exploded and blew its heatsink off due to bad motherboard caps from the dot-com fiasco. Almost did start a fire but I was right there to get it under control.
Haven't had it happen... but it's always been a joke when I'm hooking everything up. For a little while, I had a picture of tangled up wires, cables, and wall warts as a FaceBook profile pic. lol