Another vote for this. I run Aperture at home on an old Mac Pro 4,1 2.6GHz quad core with an Nvidia GTX 560ti GPU, and it runs pretty well.
At the studio we have a nMP 6-core with D500 GPU's and after using the skin smoothing brush on about 10 images, Aperture starts to choke. It takes 5-10 seconds to load the next image, and then after skin smoothing is selected, Aperture stutters for about 5 more seconds (can't move mouse at all) before you can use the brush.
It makes absolutely no sense. I started suspecting it may have something to do with AMD vs Nvidia GPU's.
I tested this by taking the 560ti out of the oMP and installing an AMD 7970. Using the skin smoothing was faster for the first 10 images. Then, I started getting stutters and pauses as noted above.
I think it's Apple/AMD's fault. Too bad we probably won't get a fix since Aperture has been discontinued