They're a nice idea in principle (and were the best option back in the mainframe era), but power electronics have gotten better faster than rotational maintenance at a datacenter company. They also weren't widely deployed enough to have a great support system, and it was firmware/software which caused most of their outages.
Dual line cord for network devices, and then STSes per floor area, probably make the most sense. Basically no commodity hosting provider uses dual line cord servers on A and B buses. I love having dual line cord for anything "real" (including virtualization servers for core infrastructure), but when you're selling servers for $50/mo, you can't.
(there's the Google approach to put a small UPS in each server, too...)
No. Incorrect. There is a reason I 100% refused to move my hosting company there. I'm not going to say anything else publicly, but it wasn't the hardware that caused repeated outages there. (I moved my hosting company from San Francisco to San Jose, and lived in the Bay Area for 10 years. Everyone in the hosting industry in the Bay Area knew each other. I also hosted for years in AboveNet SJC3, which had the same flywheel setup.)
Note: I hope at this point they've fixed the issue. I've been out of the industry for a few years. I wish them the best.
But the hitech UPS was a weak link. When they sold all their facilities to someone else (DRT), that fixed most of the other issues.