I've come to these headphones having previously used the Sony EX500 and the Sony EX300. I'm writing this review having only had them about half an hour, but I'll edit later if necessary.
First thing you notice compared to the EX500: clarity. The EX500 are pretty damn good and I had hardly noticed the small distortion, that is until I plugged these into my ears. Vocals especially now sound very, very clear, and crisp; but in a good way.
Which leads me into my next point. I'm no audio expert, but the impression I've got from upgrading my headphones is that more expensive pairs can handle more layers of sound. The EX500 may have handled vocals, guitars, and a drum beat, maybe a bass quite well, but introduce more sounds and good as they are, they get a little muddy. With the EX700, all of a sudden in one song I'm noticing a xylophone very distinctly on top of those instruments (which I couldn't hear properly with the EX500), and then suddenly there's this violin coming in crystal clear as well. I don't know that this is how it's meant to work, but that's how it sounds to me. These earphones just seem to be able to lucidly handle as many layers of sound as your portable player throws at them, all with great definition.
So yeah, they're definitely worthy of being considered Sony's top of the range in this style of earphone. At this price, I would hope so. Just a word of warning; unless you have more money than you know what to do with, I wouldn't go for these unless you're spending on average at least 2 hours a day with your earphones plugged in. You have to be able to justify the price, and both the EX300 and EX500 are still great headsets, for far less.
But yeah, if portable audio's your thing, then these are a pretty sick investment. And on the flip side of what I said, if you do spend loads of time with your mp3 player, you do pretty much owe it to yourself to maximize your listening experience. You won't go far wrong with these!
EDIT: I can no longer really recommend these after one of the earbuds came loose and was jammed in my ear for 24 hours before I could see a doctor, a most uncomfortable experience. I will instead be checking out the Bose IE2 earphones which are designed to prevent this from happening, and I have also ordered a pair of Sony MDRXB700 over ear headphones