I've owned these now for about an hour, and they sound fantastic and theh noise cancellation is excellent. One thing to keep in mind though, these things are heavy. I've been wearing them for an hour and I can definitely feel the weight of them.
I've had mine for a few months now, and I've gotten used to the weight somewhat. Coming from the Grados and Bose I had before, the weight was a bit of a shock and I had a hard time forgetting they were on my head. A few months down the road, I'm accustomed to it much more.
I do still find them uncomfortable around the ears after a couple hours, mainly I think due to the clamping force required to keep such heavy headphones in position.
As much as I like these headphones, if Apple release a lighter "sport" version like was rumored, I'd probably switch if they were lighter and had similar sound and noise cancellation quality. The fancy metal build is nice, but I'd put up with some plastic if it made things more comfortable.