I still annoy people by talking about my time at the high frequency trading firm, because working there was a revelatory experience. They were operating at a scale and velocity far beyond any place I've worked at, with lower tolerance for downtime, and very little hardware, relatively speaking. The traders had fun, of course, but it was frankly kind of boring to work there as a techie, what with everything ticking along so smoothly all the time.
And the way they got there was through an absolutely fanatical devotion to the KISS principle.