We are a Powerware house. We had a large number of 3kVA and 6kVA units in our previous data centre (no-one would stump up the cash for a large unit so we had to buy them as we needed them). After about 5 years (very rough figure), we've now had 3 or 4 units fail, sometimes in the UPS, sometimes in the bypass unit. They all seem to be component failures (in the case of the bypass unit, a leg broke off a small capacitor). I don't think we've replaced any of the batteries in that time and they're still all holding charge well, even at full load.
Several data centers at which I have been involved in the maintenance of have used Powerware UPSes. We've had great luck with them everywhere i've been, and this includes service and support. The service I have received from them (at least in the Southeast US) has been nothing short of phenomenal, including calls from the reps years after they were purchased, even on small installations, with promises made and kept time and time again. I have never been disappointed. I'd like to echo the results of other posters: We replaced Liebert with Powerware in two or three of those installations and had great luck, where the Liebert units would come out with spotty failures on a fairly regular basis (components, etc). Personally, i'd like to hear from more people who are doing serious work with DC power in a collocation environment (with the market reality of customers who want AC). I have seen customers request DC and nothing but. Tim