Just came accross Sheldon Brownes pros and cons of coaster brakes. I think it bears repeating here as so many people, I suspect, are uninformed about them.
Pro:
Coaster brakes are unaffected by weather. They work just as well in the rain as they do in dry conditions.
Coaster brakes generally require less maintenance than any other type of brake.
There are no cables running from the handlebars, giving a tidy and simple appearance.
The lack of cables is particualrly advantageous for folding or take-apart bikes.
Coaster brakes can be a good choice for handicapped riders who lack sufficient hand strength, or for arm amputees.
Coaster brakes are usually quite narrow, fit in 110-114 mm spacing , though they can be fitted to frames with wider spacing by adding washers along the axle.
Con:
Coaster brakes make it awkward to get started up, since there's no easy way to rotate the pedals to a good starting position.
Coaster brakes often cause skidding, resulting in excessive tire wear.
When coaster brakes fail (usually the result of chain breakage or derailment) they fail suddenly and completely.
Coaster brakes are prone to overheating and fading when used in mountainous areas.
Too many bikes are equipped with only a coaster brake, so there's no back-up system available in the event of brake failure.
To be safe, any bicycle needs a front brake and some sort of secondary backup braking system.
here's the link if you want to read it all.
Bicycle Coaster Brakes
