The Toyota 8" is a tough little monster, I have seen them hold up to some harsh abuse.  Although if you are running a V8 and large tire or vise versa, you could break them if you really wanted to.  Buddy of mine has a locker and the all pro axle shaft, with 37" Toyo's, and a built 3.0L and does dry pavment donuts all the time.  He did however break a 5.29 ring though  .