I found Open GL to be worse (slower) even in 10.6.3 than with it off -- I am running a 285 GTX (1gig VRAM) card in my Mac Pro. Clearly it was better than the CS4 version, but still slower than my system on screen redraws and brushes when working on large MF files. I've turned it off on both my Mac Pro and MacBook Pro installations. I suspect it is probably great for web images, but even a card with a gig of VRAM is going to be processor challenged with 100MB + image files.
As an aside, what has helped is setting cache and the new "tiles" dialog to the right spot. For me and the image files I typically work on, setting cache to 4 and tiles to 1024 size seems to be the sweet-spot, FWIW.