Originally Posted by pigmode

Sidestepping the sensory awareness issue for the moment, there are real problems with mini-style headphone usage in an enviroment with high ambient noise levels. The noise leakage from outside leads to turning the headphone up to dB levels that will eventually cause damage to the inner ear. There are high quality (expensive) phones such as those made by Etymotics that provide a good level of noise isolation, but even then I'd be wary of incipient hearing damage.