I highly recommend a search, perhaps on QC2, in the Travel Technology forum, where this has been discussed quite a bit, especially the difference between the original and the new ones.

I have the original, and here are my quick comments:

Would you recommend the produce? Yes, if you travel a lot.

Does it elimiate all sound? They only work with low, continuous noises like engine or train rumble

Does it eliminate the sound of other people talking? No, they don't cancel this kind of noise. Since they're somewhat substantial and totally surround your ears, they do deaden some noise, but don't cancel this kind of noise.

Is it worth it? I think so.

Does it really work ? Yes, but only for specific sounds.

And what is it really good for? I find that I work and can concentrate better when I'm wearing them. I also find that I feel better/more rested when I arrive at my destination. They're a nice way to insulate yourself from the world, even if they don't cancel out all noise.