Oh yeah, definitely. Especially when you add in the excessive force of large tires (35" and up) into the equation. Throw a detroit locker in there, and you are snapping axle shafts like pretzel sticks.
On my current build, I will soon be running 37" tires on a ford 9" rear and a D44 front (richmond gears front, Yukon back) with a detroit in the rear. Lets just say I will be carrying spare axle shafts, but I am not worried about breaking the gears. I am just hoping my old 360 wont have enough power to wreck stuff too bad.