I live in the Boston area. Today, there were massive delays on the T trains (public transportation) all due to a power outage. The power outage which lasted about 7 minutes, was inadvertently caused by a maintenance crew accidentally tripping a breaker at one of the worst possible times – rush hour. To get everything back up and running took about 30 minutes, but the outage brought the trains to a standstill and things took awhile to get back to normal.  

http://www.boston.com/news/local/breaking_news/2009/05/power_outage_de.html

Imagine if someone did something similar to your IT infrastructure? This is why having clear processes, good plans, and fully testing everything BEFORE implementing in production is key.