Here is a review on the Bose quietcomfort 3 from a music lover and mild audiophile.
I listen to LOTS of music, at home and on the road. To give an indication, my 80GB is 75% full. When on the road, outside noise does spoil the experience, takes away details and is tiring when background noise is mixed into the music.

Put the QC3 on, and aircraft sound moves to the background. Play music, and sound seems to be gone. Well ok, a crying baby may get through (if quieter!), but that’s a tonal range that can’t be compensated easily anyway with the current state of technology. Guess that nature designed babies crying in a way that it can be heared anywhere and at any time

The problem with this thing from an audiophile point of view is: It doesn’t sound right. Especially the mid ranges are muffled and that can ruin singing and guitar solos and the like. I even use the boost Treble EQ on my Ipod and that makes it a lot better! (omg using EQ is a sin in the audiophile world, but this headphone needs it!)

HOWEVER. This doesn’t mean the QC 3 is bad! It’s certainly TONS better than the average in ear headphone. And actually it’s good enough to reveal the flaws of 128bit mp3. And, most of all, the noise reduction of the QC3 outweighs the sound quality. I enjoy my music much more when on the road than I used to.

So, in other words, if you’re looking for high end sound at home and do the occasional travelling: don’t get this device, get Stax headphones for a few bucks more instead!
If you’re looking for noise reduction on a plane: get ear plugs.
If you love music and want to listen in noisy environments: get it, this thing must be the best for that purpose!