[dgallagher]

"At this point, the ONLY reason I've been buying macbook pros rather than low-end macbooks is the screen size."

Some of the higher-end Pro models have better video cards, which yields better 3D performance, and sometimes better output on larger displays (e.g., running 1080p video on a 1920x1200 monitor). I'd imagine Photoshop CS4 runs quicker with a better video card (assuming Open GL is enabled in PS).

A few extra USB ports on the big guys too, and semi-faster CPU's (which doesn't make a heck of a difference unless you're doing something intense).

Other than a few people who care about the above, you're right. You're mostly picking for screen-size/native-resolution, and weight/form-factor.