If you have been thinking of doing a Mud Run, put on your Nike's and Just Do It. I completed my first Mud Run last year (2011) in June. It was a Warrior Dash Event. I have to tell you that I have never had more fun running in my entire life. I loved it so much that I signed up for the next Warrior Dash in my area that was 2 months later in August.
The courses are challenging but, even if you are not in great shape you will be able to finish. There are many longer Mud Runs such as the Tough Mudder and Spartan Race that are very intense and offer longer courses (usually around 10-13 miles) There are also many other runs that are right around 3 miles and very manageable. The Warrior Dash is a great one.
If you are looking for a Mud Run, Check out the Indian Mud Run in Coshocton Ohio. It is a new event for 2012. It was organized as a grass roots effort to raise money for the local parks, and as a result all of the money raised will go directly to the Parks. It will be a great time. I plan on strapping on my GoPro video camera and recording my run. I plan on posting it here for you to enjoy.
Indian Mud Run - Coshocton Lake Park: