It depends on how "clean" your power is. But really I've never had any of my PCs run on a UPS, and never had a mobo or PSU go due to power fluctuations.. I see no need for a UPS for a PC, unless you need the time to save critical work etc before shutting down.
the biggest problem with power failures isnt when the power fails, its when it returns, most people get damage when the incomming spike from eskom returning, but the truth is most power supplies are designed to with stand an incomming spike (Well to a point), the best way to see if you need protection on your equipment is ask around the nabourhood if other people have had problems then get a UPS or surge protection if not the why bother