I still can't decide, each has their own advantages. Lightroom is a bit fiddly for me as an organisational tool and for me Aperture blows it away in this respect. However, for editing without the use of Photoshop, I think Lightroom has the edge, plus the presets in LR are excellent, yet Aperture has none. I don't like the clone tool in LR, yet find it extremely easy and effective in Aperture, plus Aperture allows you to view the photo in a large format, whereas LR and their 'full screen' is anything but.
At the moment I use Lightroom as I just feel that the final product is a tad better than what I get from Aperture.