I mean that using a low end GPU will be slower than using the CPU without a using a dedicated GPU. To get the speed benefits it appears that you need to have a decent GPU.
See this review: http://arstechnica.com/reviews/apps/ado ... view.ars/4
In particular: "Another limitation: GPU acceleration affects drawing speed. You will find that drawing is slower than in CS3 if you have a weak GPU, and the computer is under a heavy load. I discovered this while doing 3D renders in the background on a Mac Pro with an Nvidia GeForce 7300 GT. Brush drawing was slow, and when I restarted with GPU acceleration disabled, it was faster than with it on. I did some testing on my MacBook Pro, and the difference wasn't as noticeable, so it looks like the crappy Mac Pro GPU was to blame. The lesson: get as beefy a 3D card as you can afford, because it will pay off in the long run. "