Maybe can help abit here...
Motors tend to run hotter and have their lifespan reduced by abit when they are put on non-sinewave voltage sources, which is why a UPS that simulates a sinewave the closest is the best choice (with small consumer office types, this may not be perfect, but close)
For those of u who wish to have longer backup times, just use a sinewave UPS that can allow extra battery cabinets/packs, and u can just replace or increase the batteries as and when u need - the UPS is just a dual conversion device
As for APC users, please note that most of their UPS are using 'offline' technology, meaning that the inverter (converts battery power into AC normal power) is always resting when there is supply from mains. It will ONLY turn on and do its work when power fails, and if u have a crappy or worn out inverter, then there is a chance it might not do its job when the power cuts, defeating the purpose of having a UPS in the first place, which is RELIABILITY always...
My advice is to go for a slightly more expensive line interactive UPS which has its inverter working all the time, than to risk having it fail when the time really comes for it to kick in...
And btw, dont assume the backup time they quoted is accurate, because factors like motor startup inrush requirements and battery age affect the performance of the UPS, so do oversize slightly and change out the batteries all in one shot, every 3 yrs max
Hope i helped...