The phone guys have a handful of these industrial PC chassis kicking around (the type with a "PC on a board" with a bunch of PCI slots). They use them to run the "DT-24" cards that connect the IP phone system to ISDN-PRI circuits for incoming/outgoing calls to/from the outside world. The DT-24s need two things from the PCI bus -- power, and a clock signal from the "PC on a board". Otherwise, they're self-contained.
After running for since 2001, one of those chassis failed last month. The DT-24s wouldn't come up; a case of "the lights are on, but no one's home". The phone guys have the chassis in their work area, and I was poking at the insides with one of the techs yesterday. That's when we noticed the CPU on the PC on a card. There was neither heat-sink on the chip, nor fan. I think we found out why the PC card stopped generating a clock signal...
This is what happens when you run a 366 MHz Celeron for four years with no cooling beyond simple convection.
Click on the images for full-size. Notice the burnt look around the edges, and the bubbly cooked material around the pins. That cracked piece of ceramic on the CPU's underside (right image) used to be perfectly smooth. For a close-up view of the slagged underbelly, take a look here.