Interesting.. I've noticed that the bass has tightened up, seemed a little HD650'ish at first (slow), mids have alway been brilliant and the highs are smoothing out. Maybe because I was mostly using an ill fitting set of velour pads. Have the pleathers back on now and am really liking it. YMMV.. just my experience.
My experience has been similar. I've got about 50-60 hours now and I've noticed the bass seems quicker and has a bit more impact than when I first took it out of the box. Mids and highs are silky smooth. I prefer the velour pads though, they just sound more natural to me. I found the pleathers sounded slightly hollow and artificial.