I've always worked at 24/7 companies. That said when I worked at a small/medium sized company I was the only person who could support some of the critical systems *cough* database/crm/data warehouse so i was on call 24/7/365. Yes they had a maintenance window, for 3 hours on sunday night, which required me to be up to monitor..... The flip side is i got to groom myself like a wild, as opposed to city, hobo and no one complained. Now working at a large company the hours of operation are technically 9-5 but processes run all night, the flip side is there's other people so we actually have an on call rotation and can turn our phones off. I much prefer the latter even if it's a little more rigid in other areas.