I rebooted a Dell office linux fileserver once, just to ensure my new fstab entry mounted ok on startup. It didn't mount okay because I made an error in the fstab startup options. Although that turned out to be a more minor issue with the reboot, the much larger problem was that after rebooting the server it would no longer recognize any USB keyboard (I tried 5 different ones) - on any USB port - or via a plugin PCI card, and I couldn't work out any other way to give keyboard input without first having a normal working keyboard. I tried reseting the CMOS but that just resulted in the machine asking for an F-key to get pressed on startup.
After talking to Dell technical support for some time it was apparent they had no way to work around the issue either (short of replacing the motherboard) and we ended up throwing out the whole server and moving the disks to a new one.
That was a late night, and one server i really regretted rebooting!
PS We had a leaky roof and an umbrella over the server for some time, the server had got wet previously and still had drip marks all over it, so I wouldn't really *blame* dell. ..