My biggest surprise storm was in the Sangre de Christo in Colorado one September years ago. Big blizzard, stranded for a day while it blew out, winds probably 60+ mph. Our tent was a bomb shelter - a Bibler Bombshelter to be exact, and it held up very well. A hunting outfitter nearby wasn't so fortunate, and we had to give shelter to one of his clients. After the storm the outfitter bailed immediately, leaving behind much of his spike camp. We hiked out after the snow stopped,after a thorough pack-up, slowly because of the drifts but with everything intact.
Lessons I learned: (1) In shoulder seasons and winter check the weather constantly before departing. If we'd done this we'd never have set out. (2) If it's really bad, bail if possible. See Roger's article. (3) When it may snow and you are willing to risk it, take a winter tent. Whatever it weighs. Better a more difficult climb than inadequate or no shelter from Mother Nature. Safety ALWAYS trumps weight.