I have not done one, but I know friends who have, and I watched one of my friends "compete". After talking to them, the one thing I take away from it is, get some hill training in. Most, if not all, of these events are in areas that have skiing during the winter. The biggest complaint I heard from them was the running up and down hills. Downhill sounds easy, unless it is wet and slippery. For the few obstacles that are on the course, you can pretty much struggle through those. Plus, with the obstacles, you can go around some of them if you struggle too much, and can't hand climb over water pits, or go through giant pipes. There is one near me tomorrow at Yawgoo Ski area in RI. I'm going to watch two of my co-workers. I haven't done one yet, because I would probably be the one to twist an ankle and not be able to run, bike, and lift for three or four weeks. Not worth it to me. It does look like "fun" though, in a weird sort of way (i.e. "let's pay $30 to go run 3 miles in the mud").