I am not clear on this and wonder if someone here can help me understand. The 17" comes with a 1920x1200 mp screen which is referred to as High Definition. I understand that the next OS, Leopard will allow any computer to be used at any resolution so that theoretically, the 15" could be used at 1920x1200 mp resolution. I understand that this would not be very practical because the image details would be extremely small. However if one did up the resolution on a 15" in Leopard, would this make it a "high definition"? I understand also that the 17" HD has 133mp per inch as opposed to 115 or so mp per inch in the 15" MBP. Would the higher resolution on the 15 " make it appear as sharp as the 17" in the same resolution? I guess the equivalent of the 17" 1920x1200 is the 15" used at the native resolution of the 17" (1680x1050)mp. So if the 15" were set using Leopard to 1680x1050, would it appear essentially the same, meaning as sharp and clear as the 17" set to 1920x1200? Or does the 17" high definition give it a crisper appearance because the 15" is not "high definition"? Hope this makes sense. I am a bit confused. Also, if Leopard is going to allow the 17" to be used at 1920x1200, why pay the $100 upgrade today to get that feature?