Pros: Extra-ordinary sound quality, comfort and fit.
Cons: Not recommended for high impact work-outs. And this goes without saying, cost!
The bottom line: My opinion, don’t bother with other headphones that boasts a noise cancellation system. Don’t waste your time nor your effort!
Next to my M&K 750THK 5.1 home audio speaker system... and next to my Polk reference car speakers (powered by Alpine amps), The Bose QC3s are the best things that have touched my ears. Is it worth it? For $349, it better be worth it! They sound great! I’ve tried Sony, Sennheiser, and JVC noise cancellation headphones. Don’t bother! I tell people that I could NOT find reason NOT to buy these headphones. I totally adore this device. Other than using them on the plane, I use them at the weight room and for non-impact cardio. With regards to durability, I would take extra-special care with these. The hard-zippered care is ideal for travel protection and a place to store my ipod. I’ve had mine for 6-months and the battery life is still outstanding, 15-20 hours per charge (I wish my ipod had that battery life). The phones are very comfortable and fit well ON my ear (as oppose to around my ear, for the QC2 model).

With the noise cancellation engaged WITHOUT music – the cancellation technology blocks about 60% of the surrounding noise (my personal subjective quantification). Note: try this with other brands – and they don’t even come close.

With the noise cancellation engaged WITH music playing, - the cancellation technology blocks about 90% of the surrounding noise (again, my personal subjective quantification). At times I have look around the gym and remind myself that there are people around me.

Truthfully, if your looking for 100%, you won’t be able to find it.

Overall I love these headphones. And if your wallet can afford it, buy it!