Pros: Comfort. Like-- you can sleep in them.
Cons: Loose low end, Treble lacks definition and soundstage.
I bought these at an Apple store after jumping around between a few display models, and they certainly were the best of the lot that they had, in both sound quality and comfort. I didn't want to take them off, so that told me something.
What's wrong with them-- Well the mids can get mucky-- like there's a film over them. The bass is loose on the extreme low end-- it gets really slappy in the extreme lows below 200hz. The treble gives me the most bother. There's a real lack of imaging in these phones-- they bowl over the transients and there's little soundstage anywhere. Compared to my UE Reference Monitors, well, there isn't really a comparison. The UE's do everything so right, it's laughable when I jump to the B & W's.
So you'd think I'd be chucking these in a drawer and never look back, but a funny thing-- despite their shortcomings (I tend to address them with EQ- and if you want a different appreciation for them fire up iTunes and put the "electronic" eq on them and dial them in a bit) these headphones are like a comfy pair of old slippers. They don't do anything particularly well, but I find myself reaching for them often because they're so darned comfortable to wear. I can take a snooze while wearing them and they're wonderful. Beware- in warm weather, your ears will sweat!
One final note-- because of their flat profile, there are about five positions they can rest on your ear, and each sounds entirely different. Play around with placement before dismissing them, you might find a really good position and spend the next two months trying to figure out where you had them on that great night of listening they provided way back when.
Yeah, they're quirky and expensive, but they look good and feel great. I'm not getting rid of them, they're a creature comfort my ears appreciate on the right occasion. They're not for detailed listening. They're for curling up with a good book on a cold night. Soul food for your ears.