I learned the hard way going down Mt. Lemon. A 9,000ft mountain. Our Death Race 2007 was up Mt. Lemon, I missed the race due to work so I went by myself the next day. It was great going up, coming down my coaster brake got hot and just stopped working. I had to jam my foot between the tire and frame to stop. I had several close calls and even got the attention of a sheriff.
He was a nice guy, he gave me a ride back down. You know what the sad thing is. I'm still using that very same coaster brake and have not upgraded my brakes like I said I was. It did the same thing again just recently going down A mountain. Once it cools down it works just fine.