I've been using Aperture 2 for a while now and I think it does it's job well. It is a very good image asset manager with powerful metadata tools and a fairly intuitive interface. It has inbuilt RAW processing and non-destructive simple editing features and good export functionality. I was starting to find that there were things that I wanted to go into Photoshop for as I became more experimental - these were typically local changes to an image rather than global (curves, masks and layers in particular were not available in Aperture 2). However if changes tended to be global to the image Aperture sufficed for most things for me. It has a plug-in architecture which allows editing in-app with some familiar software such as Nik and Photomatix.
With the introduction in Aperture 3 of curves, brushes and essentially layers and masks (though not exactly described that way it is possible to build up an image with a variety of varying adjustments both locally and globally) as well as in-app geotagging , audio and video asset management with some editing ability, adjustment presets and brush presets it's likely that I will be able to do much more in Aperture and be less likely to use Photoshop for some time.
I'd be interested to see a comparison between Lightroom and Aperture - I don't use Lightroom but I had the impression that it was more of a complement to
PS or Elements rather than a stand-alone app but I may have this wrong (on a course I did recently the speaker kept saying LR wasn't a pixel-based program and you needed to export from LR to either
PS, Elements or another "pixel-based" application).
I suggest you work your way through the web pages on Apples
Aperture site and in particular look at the videos on those pages and if you're still interested download the 30 day trial. My copy is winging it's way out of Sydney as we speak