Thanks for the links and info. I'm looking forward to the GoRuck Challenge, it's very motivating. I've been training and actually hurt myself from overtraining during a 2mi hike with 75# on my back - I don't think the barefoot shoes I like so much are very good with that kind of load. Bought myself some cheap but stiff-ankled hiking boots today, if that makes a real difference I may invest in some good Danners or etc.
Anyway, I can see the ToughMudders and similar getting boring after a few times... but I don't think I'm ever going to be one of those die-hard ultra extreme dudes. I'd
love to do the Pike's Peak Half Marathon, just the uphill portion of the full thing, even though I know there'll be hell to pay afterwards with my knees. After the GRC I'll see what's offered and try a few of these out. If all it does is motivate me to train, it'll be money well spent.
ETA: well, that didn't last long. The cheap boots definitely helped my ankle.....but after about 8 hours of wear, they already broke an eyelet as I cinched it down. I've just ordered some Danners, and luckily REI has a good return policy.