This hit us bad.
The company I work for switched from locally hosted Exchange and Notes to Office 365 specifically on claims it was more reliable and faster (coincidentally, they also could layoff about 12 sysadmins). For the most part, it works, though with much greater latency (this is a rural area). But when there is an emergency, where multiple departments need to coordinate, it's proven useless on multiple occasions. When we have to enter data regarding an emergency, almost in real time we need 24/7 up-time. We're communicating at all hours. I work 0000-0800 CDT, and need to know that my superior knows what happens before 0500, and for the past couple years, while everything has been sent through Office 362.5, the entire emergency services department I work in has taken to defaulting to Apple's iMessage for sharing secured emergency info (which also meant everyone needed an iPhone) to make sure it actually gets through. This is entirely unofficial, of course, and despite the Idiot Tax involved, it's saved lives and likely millions of dollars since I've been employed here. Sometimes "It just works" is just what we need.