I updated my MacBook Pro 2011 to 10.6.8 yesterday and cannot boot. In Safe Boot I can for one minute. I have try a couple of things that I have found on the web but nothing work. I will perhaps try to format the hard drive and reinstall the old OS on my dvd.
I upgraded my 2011 to 10.6.8 just fine, but had to do a fresh install on my wife's 2008 WhiteBook after upgrading from Leopard (10.5.x), to Snow Leopard to 10.6.8.
I have boot with my DVD OS X holding C on my keyboard. Using Utility menu I have use Time Machine to restore my OS. Now I can use my computer but the OS is 10.6.7. After that I have try again to update but the same problem occure.
Perhaps its my Windows 7 on my Bootcamp that make the problem...
Try turning off the graphic card energy saving that switches between graphics cards to save power. The preference for this is under energy saver. Uncheck the "Automatic Graphics Switching" box.
By turning it off, you use the dedicated graphics card only. Might help...