One of our build machines was so dusty, the fan fell out of the GPU and was just hanging there by the wire. I dusted it, pulled the fan off and put it back to work. That machine is still in use, and still works even without the fan. Granted, it doesn't use the GPU for 3d, so I'm not really worried. I try to get people to dust out their machines whenever I can.
Another day one of the other build machines started to smoke. The power supply died, and rather than turning off, it decided to get hot and melt some plastic. Luckily we happened to be in the office that day, or who knows what might have happened.
We've also had someone pull his case over with his headphones, not realizing they were attached. Had someone spill coffee on one. Lost a few keyboards and mice that way, too. And we drop controllers on a pretty regular basis.
There has also been a few casualties of random ball throwing accidents. Adam caused a spill in to our $20k PS3 dev kit. It still worked after it dried out, except for the wireless controllers. We found out a few months later that it was just the wire plugged in to the wrong port. Yeah, you plug something in to get wireless controllers.