I voted absolutely none is acceptable. Now, have I had breakage since starting my HHJ? Yes. But it is not acceptable, and I know the exact cause was completely abandonding my hair care practices (though just for a brief period of time - like a week), in particular wetting my hair down without using any conditioner, leave-in or moisturizer then pulling my hair back into a bun. My nape went bye-bye! This breakage is unacceptable to me so I'm back on track and babying my nape, paying extra attention to moisturizing and sealing those strands from root to tip and using a growth aid (MN) to help it catch up to the rest of my hair. If it hadn't been for that period of laziness, I would be able to say that I experienced no breakage since starting my HHJ in March 09. I've learned that my hair loves moisture and hates strong protein, and I've figured out a good reggie from pre-pooing, pooing/conditioning, DCing, cowashing and using moisturizing styling products that when I'm on point, I get zero breakage and almost zero shedding.