I've done a couple of 100s, but I'm hoping that never happens again. I was working Quality Assurance and Systems Engineering on a project for a major customer when 9/11 hit, and exactly 1 month later, the entire team was laid off except me and the documentation writer (all four devs and both full time QA people). We had a fixed deadline to ship to that customer, Jan 1 with 1 month manufacturing lag, so I had to be done by Dec 1, and coding wasn't even complete. The substitute programmers burned the midnight oil and handed me a first working copy mid-November and I worked 117 hours that week first configuring the environment to be like the customers and then testing (tests which were thankfully mostly scripted, but there were 1100 of them), sleeping all but one night in the office, usually about 2-3 hours. Round 2 (after bugfixes) was the next week, where I tallied 106 hours, mainly because I was not allowed to work on Thanksgiving day.
I couldn't go to my managers to ask for help because a) my manager and his direct report got laid off, b) my new manager didn't know the project at all and had just been bumped from peon into management (but she eventually turned out to be the best manager I ever had), and c) training alone would suck up two weeks of my time... but 70% of QA was laid off, so there was nobody to train - everyone else had to be on board for a March product release that had just lost 1/2 its staff (again a customer commitment).
Two months after that, we hired our first 1000 workers (roughly) in India and it probably took 2 months to ramp them up. They may cost 1/3-1/4 as much, but early on many of them were worth what you paid for, which is not much. The cultural taboo of reporting bugs being an insult to the programmers that wrote the code didn't help. After about 5 years, their quality improved and then we started hiring Chinese and had a similar ramp up. Now I think both groups are quite decent, but I don't think firing over 60% of the US workforce without transitioning knowledge was the brightest way to transition to that (and yeah, that is jumping in with both feet...).