Tipping the laptop screen up and down changes how much apparent shadow and highlight detail you have. I shoot all of my jobs with a laptop on location moving from room to room. The varying light levels also really mess me up. The MacBook Pro 15" screen is very nice. With the right room brightness, the right monitor brightness, and a profile you can get decent results.
In learning about controlling color with my system I have realized it is important to maintain consistent settings with the Desktop monitor, and work in a neutral color toned room with a consistent and controllable light level. There is a whole science behind choosing the right brightness of your monitor and the brightness level of your room. I find working with the laptop that I can get the color pretty good, but the brightness and contrast of an image is almost always off if I use the laptop in the field. All the critical decisions are left to made at home, in my cave.
I only suggest all this because you've used the word "critical". I feel there is a feedback loop in adjusting images to where I think they are perfect and then making a print. It is supprising the number of times I see an image which is flat or has a color cast which does not show up until I make the print. To throw a laptop screen into the mix I feel would make the target almost imposible to hit.
-Eric
