updated 10:33 am EDT, Thu July 11, 2013
Fix also reflected in OS X Mavericks
The most recent OS X 10.8.5 beta appears to solve a problem with flickering in Photoshop, accounts say. 2013 MacBook Air owners recently complained that using some brush tools in Photoshop would cause severe flickering to the extent that the app became unusable. At the time, an Adobe representative suggested that Apple would need to fix it, since it was probably a driver or GPU glitch.
Today's anecdotal evidence appears to back up that notion. Some people have also noted that installing the developer preview of OS X Mavericks solves the error, which may indicate that Apple simply brought a tweak from Mavericks back into Mountain Lion.