Apple's latest graphics update brought a number of speed improvements to the graphics drivers, especially for games, but a few people have reported a couple of problems after installing them. One is a minor flicker on some Mac displays, and another is some sites that issue videos through Flash, specifically those at Gametrailers.com, are not working properly.
This issue is not shared among all people with the same system, indicating the problem is likely with some custom configuration. Therefore, for now try basic system resets such as resetting the PRAM, SMC, and performing general maintenance routines to reset boot caches and other temporary items, which may be contributing to the problem.
With regard to Adobe Flash, the plug-in may be affected by the update since the latest version now uses GPU-accelerated video decoding and therefore interfaces with the graphics drivers to a greater degree.
For the Flash-related issues, first try uninstalling and reinstalling the latest version of Flash, but if that does not work, try downgrading to a prior version of Flash, which does not use video acceleration.
Older versions of flash can be downloaded at Adobe's Flash Player support center.
Beyond a reinstall of Flash, the problem could be with some of Safari's settings, so clearing cookies, caches, and other Safari content may help. This can be done through the "Reset Safari" option in the "Safari" application menu, but you also may want to try a third-party cleaning utility like OnyX or MacKeeper to clear these items more thoroughly.