This week Apple released Aperture 3. I have been thinking about buying Aperture for some time although I have been pretty happy with iPhoto. However, I find that I often make minor edits to photos, usually adjusting the levels and perhaps the shadows and saturation. As iPhoto always produces a new version of the image, my photo library is rapidly expanding. Aperture stores the formula for the changes rather than producing a new image each time and so keeps the library somewhat more compact. Obviously Aperture has more editing capability than iPhoto and richer organisational capability.
Aperture 2 seemed to have got a little left behind when iPhoto added Faces and Places. I now geotag all of my photos and progressively am identifying people in my photographs. Aperture 3 adds Faces and Places to Aperture and looks like it adds some tools to help with geotagging using GPS track files.
Aperture may not run too well on my old early 2006 iMac and my 2007 MacBook is a little small but I can see Aperture being a purchase with my next Mac.