I'm using it and enjoying it. I'm not that experienced at PP stuff yet so won't comment too much on that side of things, except that being non-destructive is good for a novice like me so I can revert to the master when I lose my way a bit. Early versions of 3 did not seem that stable, but it's up to 3.0.3 now and that's running really stable for me. I tried both Lightroom and Aperture and I find I enjoy the "Apple-ish" interface of Aperture, as well as managed libraries and book-making, which is a step up from the same service in iPhoto. Full screen mode with the adjustment HUD is great to use also.
Certainly worth a download and try! I'm running a 2 year old iMac with 4g RAM and it runs sweet on that.
Hope that's of some help.