I remember a few months back when someone hit the emergency power switch to the whole floor where we host at Internap. Subsequently the backup power system had a cascading failure. Livejournal, who also hosts there, was up all night and into the next day restoring their mysql databases after a bunch of them were corrupted. I believe they had write cache turned on.
Of course our postgresql servers on scsi drives came right back up. If it wasn't for a couple of servers that won't reboot automatically if the power goes out I wouldn't have even had to go down to the data center.