As an HD 650 fanboy, I'll fall in line here, gush:
The most comfortable and mechanically well-designed cans I've ever owned. I often find myself with them on my ears yet the music had stopped half an hour ago. I was somewhat disappointed with the bass response, but then again, I am only running them through an STX amp at +12 dB (which I must say is a nice card/amp for the gamers) with stock cables. Audio/music sounds great; I leave the EQ off now.