Not choppy during normal usage (starting programs, etc) on a SR MBP, but is very choppy when dragging something into the trash. This is with the magnification turned on. Been running Leopard for almost two weeks now, so it's not an indexing issue. I've also noticed stacks is very choppy when there are lots of files in the stack, like the Applications folder. It does fine when there is a smaller number of files, whether set to fan or grid.
I'm guessing this is probably an nVidia driver issue. 🙁