The $199 software is geared for photography enthusiasts and professionals, especially those who shoot raw images rather than just JPEG, and I put the software through its paces for several weeks for a review. My overall opinion: It's solid software that produces very nice images.
If you're an iPhoto user who wants more, it's a good upgrade, though it costs $199 new. If you're an Aperture 2 user, it's a no-brainer to move to the new version. For details, here's CNET's full review of Aperture 3.
Aperture 3's geotagging tools are second to none for those who want to put location data into their photos, and the adjustment brushes work very well, reducing the likelihood you'll have to drag your image into Photoshop for fine-tuning.
If you're on the fence between Aperture and Lightroom, choose carefully, because you won't have an easy time moving your photo archive from one to the other. Lightroom 3 is on its way, so you might want to wait to see what besides automatic lens flaw corrections Adobe has in store before you commit.