Just got my K81DJ's today. B&H has them in stock again. I called yesterday and had them ship a pair to my office before they closed for the next holiday week.
Physically, they are a 'tweener' - halfway between the portable K26's & a full-size can such as my K270's. Earcups on the K81's are a bit larger than the K26's, and sit more comfortably on the outer part of my ears, but are still supra-aural. I suspect this will serve to attenuate noise better than with the K26's, which didn't attenuate at all. The non-foldable headband is a blessing, since it does not need to be unpacked, and readjusted for every use (a real pain with the K26's). The fact that the earcups turn and fold in, allow them to lie flat and fit my briefcase/messenger bag perfectly. As has been mentioned, the cord is long - too long. But that is a minor, and easily overcome shortcoming. Build quality rates a very good for a portable can.
Sonically, out of the box they are a bit boomy in the bass region, similiar to the K26's. Mids are classic sweet AKG style. Highs are decently extended without ever coming close to brightness or fatigue. Overall, a nice, cohesive sound signature with no noticable gaps. Soundstaging & positioning are surprisingly good for a closed portable headphone! The extra bass will work well outdoors to help attenuate external noise, and I suspect it will be less noticable in such an environment, as with my Koss Sportapros.
I will try them out on the subway going home tonight.