I have both Lightroom 2 and Aperture 2.1 on my Macbook Pro. But having spent the last several weeks playing with both to see which one I preferred, I've gravitated to Aperture, along with a few Aperture plugins. I hardly need Photoshop any more, even though I have CS3 on the machine.
With the Dodge and Burn plugin, plus Noise Ninja, the Nik package (Viveza, Sharpener, etc etc) and the Tiffen filters, I can do just about everything I need in Aperture, and quickly too.
I do need to flip out to Photoshop occasionally for the odd bit of specific cloning work, but mostly, everything is now done in Aperture.
Love it
Oh yes - and I moved from PC to Mac purely because of Aperture.....
PS - one other thing... I can highly recommend the following book if using Aperture:
Digital Workflow series by Focal Press: "Apple Aperture 2" by Ken McMahon and Nik Rawlinson
ISBN: 978-0-240-52039-1