noise cancelling headphones..like the ones Bose makes are REALLY bad for your ears.
Remember stells, they r noise cancelling not noise reducing.
ie lets say sound waves are sine waves that your ear hears
well noise cancelling headphones just put out inverse sine waves to cancel out the noise.
in effect your ear drum is gettin g hit with 2ice the waves (bad 
) except your brain just does not interpret that as sound. as far as the brain is concernedthe sine wave and the inverse sine cancel eachother out except your ear drum is still getting abused
I'm pretty sure that that's not correct. The whole point of noise canceling is to cancel out the sound wave so that your eardrum does not move. If your eardrum moves, you will hear a sound. So if the noise canceling works perfectly, and you don't hear anything, your eardrum is not hit with double the wave, it is not hit at all. The noise is not canceled in your brain but before it even effects your eardrum. You are correct however, that if the algorithm (the calculation of the necessary phase shift) does not work perfectly, in the worst case, 2 times the wave will hit your ear drum (which however you will then hear just as loud).
Having said that, I would still recommend in-ear buds over noise-canceling headphones. Much better noise reduction and thus, much better sound quality in noisy areas. My old etymotics came with rubber ear buds (in addition to the silicone ones), which really blocked out almost everything except normal speech. For all kinds of headphones, I can also recommend this site:
http://www.headphone.com/Here you can find the in-ear buds:
http://www.headphone.com/products/headphones/in-ear-monitor/
