Recently, I participated in a Tough Mudder event. The event was truly awesome once you get past the first mud event! After that, it's all fun and games.
I recommend following their training guide online @ www.toughmudder.com
It is intense so I would recommend starting more than 3 months out on training. No one on our team completed their training guide as it is, but it definitely helps if you use it as a guide. As long as you have a team or someone there helping you it is not that bad in terms of strength needed. Most people had issues keeping up with the mileage length. 11+ miles and 20+ obstacles can be very fun though - worth a try!
Check the video I made from when I participated: