I'm a big dude as far as skiers go, 6' 2" and somewhere from 180-190 lbs. I've been skiing on K2's since long before i rode for them, they were the only skis i wanted to be skiing on.
The ONLY K2 I have ever broken in my life was an '05 Public Enemy that i purposely mounted forward of center to have slightly longer tails....
I usually ride the same pair of skis all season (and all summer). To me, k2's are incredibly durable. I've used a pair of the exact same Hellbents for 3 seasons in a row, not necessarily "taking it easy" on them either. Most of their skis I prefer are pretty soft, and I think it's logical that softer = a lot more difficult to break. Love those skis, I'll ride em till I'm old and grey