I bought the first Bose noise cancelling headphones, the QC-1 in 2000. The big, clunky, non folding model. They were still working 8 years later when I began looking at replacing them. I A/B'd my old Bose headphones against most of the other manufactures at an airport store and found the old Bose to be the best - others were getting close though. Later I passed by a Bose kiosk (I think in DIA) and wanted to see how my old ones stacked up against the then new QC-2. The new ones were definitely better (and they folded flat). I am now the proud owner of QC-2's. Bose gave me a deal I could not refuse - trade in my 8 year old headphones, and for $100 they gave me brand new in the box QC-2's. They now have an extremely loyal customer.
Bose are not cheap. When I first bought them, there really was no competitive product to choose, so I had to bite the bullet. I am now going on my 12th year with Bose with not one problem, and great sound.
People do bring up the issue about carry on space. Quite frankly, I agree. If I didn't listen to music as much as I do, I probably would not spend the money on a set of Bose, but I do and they're wonderful.