I absolutely love it. I downloaded the trial version, and it's so much further ahead than regular photo management software that I'm beginning to wonder how I kept track of my shoots to this point. It's elegant, and even with the ridiculously high hardware requirements, it runs flawlessly. I've only had it a couple days, but I might have to buy it when the trial runs out.
Maybe it's just the loupe tool or the way the control box emerges so easily when I hit "h".
Having used Aperture, how do you feel about it compared it programs such as PS and iPhoto?