I have a Macbook Pro 15" 2011 with Radeon 6490m graphics, fast hdd and 8Gb RAM. It came pre-installed with Lion but the interface was like dropping frames *all* the time, opening Mission Control, even by just moving the mouse pointer over the Dock. Safari scrolling text used to drop a lot of frames too. I observed the same behaviour with a clean install of Mountain Lion aswell, and even my old Powerbook G4 had a faster (less laggy, frame-dropping) interface !!!
I took it to repair in an Apple authorized center in a Apple-only store in Copenhagen, Denmark, the whole inside with the graphics card was replaced because Flash colors would blackout sometimes too.
None of this worked, I guess the fault is with the new graphics drivers/architecture coming with Lion!
I had to go the unsupported route and downgrade to Snow Leopard which involved a lot of hassle but now at least the interface is blazing fast again and I don't feel my 2200 Euro macbook pro is slower than 300€ laptop PCs anymore. And I get the bonus of Quicktime 7 features not ported over to Quicktime X.
Will one Apple engineer please create a ticket for this "defect" with their internal teams?
If there is a better avenue to communicate this to Apple OS X engineers please let me know !
MacBook Pro (15-inch Early 2011), Mac OS X (10.7.5), Happens to Mountain Lion 10.8.2 too