Previously Apple acknowledged that some Mid 2010 15″ MacBook Pros (model MacBookPro6,2) may intermittently freeze or stop displaying video. In some cases a kernel panic would occur, followed shortly by the display turning black or gray.

Apple’s fix for this was to upgrade to OS X 10.7.3 or later (including 10.8), or install the MacBook Pro Video Update 1.0 for those running OS X 10.6.8.
http://support.apple.com/kb/TS4088

It has recently been reported that some owners of this particular MacBook Pro model are experiencing this problem after updating to OS X 10.8.4. Those affected are hoping Apple will release a patch soon. Possible workarounds include downloading and re-applying the OS X 10.8.4 Combo Updater, or going back to OS X 10.8.3 using a restore from backup.