Pros: Look great
Cons: small cans, claustrophbic sound, muddy and unclear.
About me: Newbie audiophile at best, I've been rocking a set of Senn HD280s in silver for probably 7 years. I have never had an issue with build quality or sound quality, and have loved them since I got them. At the time, they were a good bang for the buck, and I still think that they sound great (at least my pair does!). I run sound from a MacBook Pro, and iPod Touch (gen1), and iPad (gen1) or my LG P999 through any number of players.
About the headphones: I was looking for something over the ear and closed that had good sound but were a bit more street stylish to wear out and about if I didn't feel like having my Klipsch Image x10s stuck down my ears. I did some reading on the Phiatons (on here and Headphonia) and they seemed like something that might fit the bill.
The phones do look great, but they are MUCH smaller than I expected them to be, and even for my 'normal' sized ears were either partially supra-aural, or circumaural if i fidgeted a bit and got my ears pushed inside. Once they were in this position, the top tips of my ears were seated against the driver cover. They are not particularly uncomfortable in either of these positions as the cushions are soft, but they are not exactly what I was looking for. Anyway, after a few minutes I stopped being perturbed by this, and you probably will too if you think that the rest of this paragraph has sounded a bit too whiny.
The sound, however, is something that I have not been so easily able to dismiss. It should be noted that these have only about 15 hours of burn-in time, but I have not noticed a ton of improvement in their incredibly claustrophobic sound stage and muffled... everything. I am still surprised at the positive reviews that these cans have gotten, and perhaps more burn-in will improve things by impression is that they are muffled and lack detail across the spectrum. With no EQ on, I find that details that I can hear clearly on my 280s are simply not present in the MS 400s. I think that everything from the Low-Mids to the Mid-Lows are overemphasized and sloppy, without any high-range details to help define the texture of drums, bass, or vocals.
I am going to give these a bit more time to break in, but unless there is a dramatic improvement in sound, I can't see these being worth the price no matter how cool they look. Perhaps you could use the shell for some other drivers (I'd love to throw my 280's in here and keep my new M50s for home use) but for $200 I think that project is a rather moot point. I will probably be sending them back and just take the loss in cost of postage as punishment for buying with my eyes and not my ears.