Today I was using time machine and an usb external HD when my 15" MBP (osx 10.5.7, 2.5ghz, 4g ram) screen went black and the external drive shut down. I was using the 9400Mgt I sat there wondering what was going on when the screen came back up as if nothing had happened (my initial guess is video card overheating?). No data was lost and everything seemed normal when the screen came back up. This has happened on more than one occasion while backing up but so far there seems to be no loss of data or harm to the hardware. 
I was wondering if anyone out there has experienced anything like this and if they might have some suggestions for avoiding this in the future.
I was wondering if anyone out there has experienced anything like this and if they might have some suggestions for avoiding this in the future.