I went out and practiced this the other day with one of my former students who I still give flight reviews to. We did it in a 172 and determined that 500 AGL was a good altitude to turn around. 400 feet AGL was the actual altitude but we added 100 feet to get his bearing if it should ever happen in real life. I reminded him that, like any manouver, you have to practice on occasion. And like every takeoff, you should go through your mental checklist in the run up area addressing the various scenarios that could happen during and after the takeoff including an engine failure.