I notice people indicating that using play mode maximized was preventing the lock ups while play testing. So I tried and after nearly 40 minutes of play testing I did not have one lock up while running the game window maximized. This would seem to indicate the problem lies with the Unity GUI itself. That got me thinking about what it might be. For the unity folks reading the thread, Mavericks added timer coalescing and I am wandering if the unity interface is using high speed timers to keep the live areas (heirachy, inspector and profiler for example) updated? How many timer request could be getting slammed together with the coalescing feature of mavericks and thus hammering the windowserver process? This is just speculation but after that long run with no issues when I used the game window maximized and then having a lock up within minutes of returning to editing and scene creation/modification really makes me think it is the unity interface itself that is at issue.