The Mission Control lag may not be inherent to OS X Mountain Lion but rather to certain Macintosh specifications, such as iMacs with ATI graphics, or the new MacBook Pros with Retina display.
Tests conducted by Softpedia on a new-generation iMac (Late 2012) pre-installed with OS X 10.8.2 (build 12C3103) have revealed that Mission Control works flawlessly on this new configuration.
The same OS X version, however, is giving headaches to owners of other Mac systems, like the Retina-enabled MacBook Pro, as discussed by some users in this thread on Apple Support Communities
While the latest MacBook Pro comes with similarly powerful processors and RAM, the sheer amount of graphical processing needed to output video on its Retina display seems to induce the same graphical glitches. A video on YouTube
uploaded by a person using the Internet handle “yaoijonge” shows the bug in action.
We’ve also been able to confirm the Mission Control lag on our very own Late 2009 iMac, which boasts a dual-core Intel processor, 6GB of RAM and 256MB of VRAM – ATI Radeon HD 4670.
While these specs are certainly above the limit imposed by Apple for running OS X Mountain Lion, the graphical glitches involving Mission Control and Space swapping are more than visible on this system.
However, on the newer iMacs which use NVIDIA GeForce GT 640M 512 MB graphics, these bugs are nowhere to be found. Apple hasn’t expressly stated whether the OS X build shipping with the new breed of iMacs packs any graphical fixes.
It is possible that Mountain Lion’s system requirements need to be revised by Apple, as systems whose resources are not pushed to the limit also seem to work well.
For what it’s worth, Apple has just pushed out the seventh beta of OS X 10.8.3. Hopefully they’ll get around to fixing this issue for older systems as well.