[Rain Man]

I walk 4 miles a day with a 15" laptop and it's not a problem once you get used to it. It's exercise. However, I've got a nice backpack that's designed for it.

I like a bigger screen and think the screen size outweighs the portability issue, even in my case. The only time the size is a problem is on planes, when I often can't open it all the way because the dipstick in front of me always thinks he has an obligation to recline his seat all the way back the second the plane gets off the ground. If your son doesn't fly much, he probably doesn't need to worry about that, though.