I've seen/participated in the applause many times but all were stressful or emotional flights:
-Landing in Chicago after the most turbulent flight I have ever been on, with a measly 8 passengers in an ERJ 170; it was an early morning flight and the FA's stayed strapped into the jump seats for the duration. Really the only time I have ever thought we would actually die. One of those with the sudden 2000-foot drops... over and over again... light PAX weight made that plane bounce around seriously.
-Pilot seriously overcooked the landing on the southern approach at DCA; anyone who'd ever landed there more than once or twice before knew he was going in too high, too fast and since it was not a windy day, no real reason for it. It was a real "The batchute, Robin!" kind of landing and not pretty at all; PAX burst into applause when the plane finally stopped and the FA's announced to take extra care when opening overhead bins "because after a landing like THAT, everything's shifted."
-The first 3 weeks or so that DCA was open again after 9/11. Remember that was the last major airport to reopen. I flew a lot in those first few weeks and people applauded after every single landing. Not sure if they were being extra patriotic, or just thrilled to NOT have to drag their arses out to IAD any more?
-The first 2 months or so that MSY was reopened post-Katrina there was applause on every flight that I was on, and even now there's the occasional fit of appreciation for the city slowly limping back to life