I've had my helmet for a few years and I'm quite comfortable with it. However, the fellow who taught the urban biking course I took a few years ago said that the plastic in the helmets would deteriorate over time and not provide as much protection. He recommended replacing helmets every 2-3 years, if I recall correctly.

Does anyone know if that's true? I want to be safe, but I don't want to spring for a new helmet if it's not necessary.