updated 10:06 pm EDT, Mon October 14, 2013
Forum threads indicate unaddressed flaw in some AMD cards or Apple graphics software
Detective work and anecdotal evidence by users in an Apple Support Communities thread about problems with discrete graphics cards in some MacBook Pros has narrowed down a range of possible flawed cards (or flawed switching software controlling the cards' use) in machines from early 2011 that use Apple's automatic switching between an integrated graphics chipset and a built-in discrete AMD card. Owners with the AMD Radeon 6750M GPU seem to be the most affected, but other Radeon cards are involved as well.
AppleInsider reports that data compiled across a number of similar Apple Support Community threads by another forum user named "saramwrap" shows that owners of the early-2011 15- and 17-inch models with the AMD Radeon 6750M chip appear to most consistently display the problem, but other models that have the combination of integrated graphics and the AMD Radeon models 6490M and 6970M also seem to be likely to have the issue.
Still unclear is whether the graphics issues -- which include banding, image distortion, discoloration and sudden freezing -- are caused by the AMD cards themselves, or by Apple's software-based "dynamic" switching between the integrated chipset and the AMD cards, a feature that was introduced in 2010. Using that feature automatically moves between the two graphics systems based on what a user is doing; if they are surfing the web, the integrated chip is used but upon switching to a 3D game, the discrete card kicks in (as an example).
Prior to 2010, owners had to log out and log back into the machine to switch from the integrated chipset to the discrete card. In typical use, a discrete card is rarely needed except for 3D gaming -- thus the reason why more Macs no longer offer discrete video cards anymore. According to the compiled data, in some cases using a technique that forces the MBP to exclusively use the integrated chipset has fixed the issue, but it is not a panacea for the problem.
Worse, owners who are out of warranty often find that the primary fix offered by Apple is a logic board replacement, which costs more than $500. The company has not officially acknowledged the flaw -- perhaps due to a lack of compiled data on the problem up to this point -- but has been known to arrange a program where specific affected models can be brought in for a free repair, even if they are out of warranty. Users who already paid for repairs are generally compensated for their expense under such programs.
If the root problem turns out to be Apple's switching software, the issue should be able to be resolved through a software patch the company might issue at some point in the future. A similar problem with some 2011 MacBook Pro models was thus fixed with a special build of OS X 10.6.7. Apple has made graphics testing one of several areas of focus during the beta period of OS X Mavericks as well as recent versions of Mountain Lion, but to date there has been no sure cure other than logic board replacement.