Only one and quiet recently. Thai Airways A380 just about to land at Heathrow. We must have been very close to landing (night time), I don't know the technical term for it but the engines had gone very quiet and clearly we had pitched nose up (flaring?). Next there there was an almighty roar from the engines, tremendous sense of 'push back' into my seat and off we went back into the sky. About 30 seconds later the pilot came on the intercom and apologised saying the runway wasn't clear. All handled very professionally as you would have expected, no cause for concern from any of the passengers that I could see. Quite impressive actually to feel the power surge from next to nothing to being pushed back into the seat.