When I first got my Haymaker 1500 about 2 years ago the BB crank interface was the Truvativ powerspline pattern. In the first winter my left arm came loose when it was cold (-15*C or so). Since it was cold I wasn't really looking at my bike that much and the bolt loosen up and the arm began to wobble. This led it to damage the interface of the arm. After using some tin shivs to take up the slack and allot of red threadlocker on it (which I did in my place and gave it a day to warm up first and another to set, and used put more than enough torque on it), and then it was good until 2 months later were the bolt loosen up again (but with only a slightly wobbling of the crank arm) despite all the red threadlocker on it. Tried to fix it again but the 8mm bolt (old) broke off into the BB with out any real force. So, I got a new BB and left arm and it was good for for 3 months in the late spring, same thing but with the right arm. The arms interface was fine (caught it early, so no damage). I got a new bolt this time with thread locker, 40Nm of torque, and gave it 2 days to set. It was fine for 5 months when it began to wobble again and this time the bolt broke off into the BB when I was riding.
Since then I replaced the BB interface system with the Octalink and I haven't had a single problem in the last few months.
So are powersplines really this bad, or did I just have a lot of bad luck?