We were all-hands-on-deck for Y2K at WebTV, with Operations, devs, and management all waiting for a scramble signal from QA if something went wrong. Since, like most businesses, we’d fixed everything we could think of well in advance, I was hanging out in a conference room with my 4x5 view camera taking pictures of whisky bottles (and a mildly-cute girl from another group who wandered in at some point; portraits only!).
Turned out there was exactly one thing that had been missed: trying to add a credit card that didn’t start being valid until 1/1/2000. This produced a legendary flaming email from Steve Perlman, which was preserved for posterity because it was a reply-all that CC’d the Remedy ticket system.