I just rebuilt an old Shimano coaster brake at the shop... despite being at least 40 years old it was still pretty fresh looking and showed minimal wear inside.

I have seen coaster hubs where the shoes have been blued because of the heat and done some descents with a coaster where the hub shell was so hit it would give you serious burns if you touched it... and by the bottom of the run there was almost no braking to speak of.

I used to run a Friday night clinic for fixed gear riders and we'd do tests of brake equipped bikes vs non equipped bikes and the stopping distance of the brake equipped bike was half of the brakeless ones... in an urban setting this could be the difference between life and becoming road kill and as a messenger I always rocked a front brake. I use this as an example as the stopping ability of a skilled fg rider and a person with a coaster brake is about the same without a front brake.

Needless to say just about all the hipsters who came in insisting they were fine without a front brake decided to install one.