Definitely not a theoretical risk... as being in computer related work for the last 20 years I've seen a dozen machines fail due to power issues (lightning strikes mainly). I had a customer *using* a ups who had his motherboard, drive and mostly everything fry (the cdrom still worked) after a lightning hit. Despite having backups, he needed to recover the last day's work which forced him to send his drive out for full recovery for several thousand dollars.
I had a customer with an office of 20+ machines have half of them fail when lightning took out their main panel. The machines that survived were ones with UPSes.