I've been using Sony MDR-V600 headphones since high school. I remember in 1990, when I was a sophomore in high school, and a friend of mine had just gotten back from his first year at UF. He had his Discman with him and told me "dude you have to hear this." It was Nine Inch Nail's Pretty Hate Machine. It blew me away. What also blew me away was my friend's headphones: Sony MDR-V600's. I knew I had to have both that CD and those headphones. I got the CD a couple of days later, and the headphones the next year ($100 headphones aren't the easiest to come by for a high school kid, especially back in 1990.)
I've been a huge NIN fan ever since, and I had those V600's for eleven years. They were with me on numerous cross country trips from my home in Florida back to Caltech in L.A. By 2002, they were in terrible shape, and my girlfriend bought me a new pair (just a few months before we got married.) I've had those for almost five years now. So I've been a V600 listener for almost sixteen years.
But now I have those fancy Bose headphones. At first, I didn't think they sounded as good as my V600's. I think part of that was because I had been listening to the same headphones for sixteen years. Another reason was because the QC3's needed different equalizer settings the V600's. Again, when you've used the same headphones for sixteen years, you forget about changing the equalizer. For what it's worth, the QC3's needed more treble and less midrange than the V600's. Finally, the QC3's are less sensitive than the V600's. It's a common stereo salesman trick to use the higher sensitivity of a speaker as a way to "prove" the speakers sound better and are worth the extra $$$.
Now I actually think the QC3's sound as good as the V600's. I think the midrange and treble are a little clearer on the QC3's, but the V600's have a little more detail on the low-end. The QC3's are punchy on the low-end, but lack some detail. This is pretty typical of Bose, from what I hear. These are the first Bose products I've owned.
The QC3's are really comfortable and the noise cancellation is excellent. They also seem like they will be more durable. I've gotten a lot of use out of the V600's, but their headbands and ear cushions fall apart pretty easily.