Hi, I've just gotten a beast of a iMac, but I'm having a strange issue in Lion. When scrolling on both Chrome and Safari the scrupling seems laggy or choppy. When starting to scroll, it may seem fine, but it gets choppy or laggy towards the top of the page. A little bit hard to explain - but I'm guessing that if somebody else had the same issue. They would understand the problem from what I've explained.
I'm on a 3.4 GHz iMac, lots of memory. Using a 'magic' mouse. Obviously not so magic it can't stop itself from lagging!
Verify that it's only happening in Safari/Chrome. Open up like a Word Doc or TextEdit if you don't have word. Type a bunch of stuff (or copy paste) so that it creates a scrollable document. see if the Scrolling is choppy there. This will tell you if the problem is Hardware related/happening in the entire OS.
If it's only happening in Chrome/Safari verify that in the settings you don't have the option for smooth scrolling is checked (or try it unchecked). Sometimes in browsers (noticed mostly in Firefox) there's an option for scrolling line by line. This is so you never have half a line showing on the screen, but to someone not expecting it it looks choppy.