i dont see any confirmation that this is fixed in ML. anandtech said its improved in ML but definitely still not smooth. will further iterations of ML fix it more? who knows. i hope so but according to anandtech, he said the hardware was already pushed to the max and theres nothing that can be done about it.
It looks like the scrolling issue is fixed by leveraging the GPU moreso than what the current implementation which relies more on the CPU. The scrolling issue is completely fixed in Mountain Lion according to Apple (you should expect 30+fps performance). I have not seen anything anywhere that says the OSX UI sluggishness (read: toggling Mission Control, resizing windows, other UI animations in OSX, etc) has been addressed, unless Apple wants you to infer that is the case based on the "Smooth Scrolling" feature outline.