I've been running a 21" monitor, comp~550w/PSU, 150w pump, and my cube fridge all on a 1400va APC brand UPS for over a year. Not one problem. I get about 30 min on backup. Setup so that windows monitors it and shuts down after 10min if I loose power. Windows XP even had the driver so I didn't have to load their crappy utility.
Granted the UPS I have retails for ~$650. But when you get it second hand for nothing, replace one stuck relay ($5), and have a like new UPS.
I don't know if it would be such a good idea with a cheapo UPS.
Hope that helps.