While not quite as big as this guy, there is a off-road triathlon series called the winter challenge (
www.winterchallenge.com) and at Tsali (Tsali Challenge sponsered by the Nantahala Outdoor center (
www.NOC.com). The three events are trail run, flatwater kayak and mt bike. These are sprint distances (run 4-7 miles, kayak 3-6 miles, mtb 10-13 miles). Really fun! You can do it in teams or singles.
There is also adventure racing.