An "analog" photography veteran friend recently decided to start retouching his slowly growing digital photo collection. He bought a 27" iMac and came to me for advice. He originally wanted to buy Photoshop, not knowing about the non-destructive workflows of Aperture and Lightroom. I got him to look at both and he decided to go the Lightroom 4 route.
Having myself used Aperture since 2, I kind of discovered the software alongside him just to get him going. I'd tried the demo of version 3, but not for more than dozens of minutes at a time. Once the purely file management issues aside (where I find Aperture far outshines Lightroom), I was smitten ! Lightroom 4 is a wonderful photo editor, miles ahead, unfortunately, of Aperture. Grad filters, adjustment brushes, lens distortion and color fringing... I was stomached that I have 10 000 shots in my Aperture library.
Anyways I've kind of decided that I'll hold out until Aperture 4 or X is announced to see what it offers, but if it falls short then I'll buy Lightroom and start using that. I still have Apple to thank for pushing this family of software, but Adobe knows digital retouching and photography like no one else, and Lightroom 4 is a brilliant proof of that.