Actually I was around at the time -- it was a pretty controlled environment. A certain library was stripping characters from some links in admincp so we upgraded that.. we also put a squid caching proxy in -- server admin made a small booboo.. we were back in a couple of minutes but MySQL was spewing out errors
So it appeared more ugly than the situation actually turned out to be? Those errors can be a pain in the rear.
Biggest oops: Installed this plugin that made a bunch of errors (broke the board). Was pretty easy to fix, but biggest problem I ever had.. so far.
My biggest OOPS happened just recently, I was working on my test site, checking out a new template modification which for some reason wouldn't work when I viewed the page. I realised about 4hrs later, when a member of my team rang me, that I had actually modified the "Live" site and not my test site, everything was a mess and it took me another hour to fix it. I now know viewing your "live" site while working on your test site is not a good plan.