Some owners of the unibody (late 2008) MacBook Pro notebooks may have discovered an issue with the screen, as a number of users have reported that the display will suddenly begin blinking/flickering.
Per MacFixIt and the Apple Discussions board, one poster described the situation as follows: "My computer had a hard time digesting all of the new messages being added in Mail. Everything slowed down temporarily and Mail disappeared and was inaccessible. When it finally reappeared with the new emails, I noticed the intermittent blinks."
The issue seems to occur randomly, though some users have stated that the problem emerges during heavy workloads. In some cases, the problem may only occur once or twice, while for others the blinking occurs rapidly, accompanying significant system slowdowns.
As to the source of the problem, the current thinking on the issue per the discussion board is that since the issue is found only on the MacBook Pro notebook, it has something to do with the graphics drivers working to manage the dual graphical processor unit setup. Non-Pro MacBooks have yet to experience this issue and the problem seems to occur when users are utilizing the GeForce 9400M integrated GPU, which gives it the same graphics configuration as the non-pro MacBooks.
Reset PRAM: Users can reset the computer's parameter RAM by rebooting and holding the options-command-P-R keys until the machine cycles through a few restarts. Then let the keys go and allow the machine to boot properly.
Reset and adjust display settings: Open the "Displays" panel in System Preferences and toggle between a few resolution settings. Additionally, users might try clicking the "Detect Display" button.
Workaround: The problem seems to disappear when users run off the dedicated GeForce 9600M processor, and it is recommended to do this unless battery conservation is of the utmost importance. Using the dedicated graphics processor will also increase the computer's performance. To do this, go to the "Energy Saver" system preferences and check the option to enable "Higher Performance" graphics. Logout and log back in again to see the change.