This is on a last-gen MacBook Pro 17" (2.6GHz Core 2 Duo, 4GB), OS X 10.5.5.
I downloaded the 0.8 Mac binary version (which I notice is PowerPC only, so it's running under Rosetta--I'll try building it later when I get a chance).
The drag-scrolling is nifty, and works great. And scrolling with the keyboard still works fine.
But scrolling by scrollwheel, or two-finger mousepad drag, is incredibly slow. I've got a comic that's about 1400 pixels tall, and when I look at it at 100% zoom in a maximized window (which should be around 1100-something pixels), it takes 13 seconds to scroll from the top of the page to the bottom. It's jerky, I get the spinning beachball a couple times, and the CPU usage jumps from 2% to 40%.
Needless to say, Comical 0.7 doesn't have this problem, nor does Preview, FFView, or ComicBookLover.