I have done my homework and completed the benchmarks to see the performance difference between open and closed clamshell mode on my MacBook Pro 15" 2011 2.2Ghz. I followed the exact instructions on this macrumors thread: http://forums.macrumors.com/showthread.php?p=12184995#post12184995 I am using Handbrake with a .txt log for each encode. The result on witch i rely is the average frames per seconds that were encoded on a specific video. The average frames per seconds is directly related to the total time taken to encode a certain video. So.... encoding the exact same video from the thread above, i get the following results: Opened Clamshell = 37.82 fps Closed Clamshell = 30.25 fps This is a 20% performance loss in closed clamshell mode if you compare to opened clamshell. It is important to note that both tests were started with the MacBook Pro's temperature stabilized with idle load. This video lasts only 10 minutes and is encoded on a MacBook Pro 2011 2.2Ghz in around 5 - 7 minutes. Since the computer takes a certain time to reach peak temperature, the performance loss should be higher on a full length movie. If you also have a MacBook Pro, i'd like to see the difference while encoding with closed clamshell and opened clamshell. Regards.