I'm one happy camper right now.
My birthday is a week from today, and my girlfriend couldn't resist but to give me my present a week early. As I peeled back the corner of the wrapping paper, I see that infamous "S-Logic Plus" logo and proceeded to go ape crap. I've been eyeing some Pro 900s ever since I got my HFI-580 back in February. The 580s had nicely detailed bass, but didn't quite have that punch for times when you just want to rock out. The Pro 900s, on the other hand, truly have head-shattering bass. Holy moly it THUMPS. No way you can sit still listening to these.
I let my girlfriend try them to a bit of Daft Punk to see what the fuss was all about. She said, "they sound like you're travelling in a bass spaceship."
I'm listening as they burn in now and throwing lots of my hip-hop and electronic collection at them: Daft Punk, Flying Lotus, James Blake, Cunninlynguist, Wu-Tang, Black Milk....and have the biggest perma-grin. I remember my 580s changing dramatically with burn-in (I was very disappointed with the mid-range initially), so I can't wait until these settle.