Pros: First class noise reduction circuitry, great design, good tight bass response, great battery life
Cons: Very expensive. Bass sounds could be a little less muddy sounding and more defined.
The bottom line: If you want serious noise reduction, or you need headphones for listening in a plane, get these. Top notch!
Got a pair of these headphones for free (through AMEX reward points), and have been using them for almost 3 months.

As much as they are very expensive, $350, I would say that initially, I would give them a 2nd thought in terms of spending the money (and draining the wallet!) for these unless I actually heard them or tried them for some time before commiting into such a hefty price. Thankfully, Bose lets you try them for 30 days risk free before you buy them.

I read so many reviews about it, where it's generally divided into people that love Bose and their products, and people that completely dislike the brand. This is my first Bose product so far.

I've been doing a fair bit of travelling lately (around twice a month), so these headphones have come extremely handy for listening to music on the plane.

So let's talk about the visual and ergonomics aspects first.

The first impression you get, before even putting these on, is that these headphones sit "on" your ear, and they are a bit smaller than their predecessor, the QuietComfort 2 headphones (which have a much larger cup that encloses your ear).

Comes in with a nice black pouch, in which the headphones can fold flat and fit nicely into it's case.

Another feature that I found cool, is the fact that it comes with a lithium ion rechargeable battery, that is good for around 20 hours of listening. I haven't accurately measured the battery life of these, but I can listen music at work, for around a full day, from Monday through Friday, and I won't need a charge. So battery life is very, very good, and if you charge them every so often, you will not worry about it not lasting long. The battery detaches from the right earcup, and you have to place the battery into the charger.

Charge time is pretty fast, around 1.5 hours to get a full charge.

The charger has a red LED to indicate if charging is in progress, and turns off when the battery is charged. Nice feature!

The ear pads have a very expensive feel, the leather that Bose has utilized is a very soft leather (not sure what type, I'm not a leather expert) but it feels very soft and feels thin, but durable. Placing the headphones over your ears, after adjusting the band is a real pleasure. The headphones fit nicely on my head.

Turning on the headphones, via a lighted switch on the right ear cup, will turn them on. Note that the QC3 need battery power to operate, meaning that if the battery is dead, or if the power switch is off, you will not get any noise reduction or any sound. Some people find this annoying, but I find it to be no problems at all whatsoever.

The switch light flashes when there is less than 4 hours of battery life left, and lights up a dim red when on and in operation.

As soon as you put on the headphones but don't turn them on, you will notice a slight rumble on the background, that I think it's produced by natural echo on the ear cups themselves. This is a lot more noticeable when you are in a noisier room or in an airplane.

But anyways, once you switch them on,... wow. You can hear some sort of a very light hiss that mutes the background noises and the slight rumble is totally gone!!! I have used these on the plane many times, and wow, I can say that the noise cancellation circuitry is very well turned for cancelling airplane background noises. I must say a 10/10 for noise reduction! The background clatter just mutes down (it doesn't disappear completely), but conversations next to you, feel like they are distant now.

I have compared the noise cancellation with a Sony headset, and the Bose totally edges the Sony out. I would say, the Sony was a 5, while the Bose is a 10.

So, in terms of noise cancelling, it's truly amazing and it really isolates you from the world around, when it's turned on.

Now for sound quality, I read so many reviews in which people complained about the sound of the QC3, saying that the QC2 are much better in terms of bass and treble clarity. I still have to try the QC2 for a longer period (more than 10 minutes in the store), but side by side, the sound quality is pretty much comparable.

One of the main gripes, is that the trebles are not extremely sharp on the QC3 as far as I have noticed, and sometimes the bass sounds muddy. But, with a little bit of equalization and bass boosting, and treble adjustments, these headphones sound top notch. You can actually feel the bass.

Also, the noise reduction doesn't interfere much with the sound quality. It's hard to describe sound characteristics on a written review, unless you can really experience them by yourself.

The headphones are pretty powerful, and whenever I use them with my iPod, I don't really have to crank the volume much to listen to music, and isolate myself from the world, so in terms of sound amplification, these are excellent.

As for now, in the 3 months that I have been using them, they are great. And, I would have in no doubt, payed the $350 for them.