Didn't want to create a new thread just for my blabber, and so I'll just revive this thread.
Got the chance to audition the HD800 today in an ideal environment (the Sennheiser showroom in Aoyama, Tokyo) connected to some high-end Japanese stuff (sorry didn't really pay attention to the equipment, but they were those big desktop amps, and they even had a Wadia dock so I was even able to use the Apple lossless stuff I had on my iPhone).
I'm not good at describing my impressions of stuff, so I'll keep it short, REALLY short.... it goes like this...
WOOOOOOOW!!!

But seriously, just insert good audiophile virtues right there, and most likely the HD-800 has that.
EDIT: And btw, I just read the Ken Rockwell review now... what upper midrange boost is he talking about? I have this BAD HABIT of checking freq response by tones, using my ears (don't worry I use moderate volume hehe) whenever I get curious about the FR of a pair of headphones. Certainly the HD-800 is the flattest I've heard among headphones that I tested using this CRAZY method. The one thing I noticed, though, is that it doesn't boost the 8KHz region unlike many other headphones apparently so that the treble doesn't "bite" much. But in any case, I didn't even think much about the result of that test-tone thing, with MUSIC the HD-800 sounded absolutely amazing IMHO.