rolling backpacks just aren't practical. first, you have the noise problem (as egfmba mentions), with the clackety clak clackety clak, and such. not only that, but if you have your laptop in it, all the bouncing might do some damage after awhile.
second, rolling backpacks look nerdy. let's face it, you may be past the "trying to be cute" phase in life, but jeebus... paying attention to style should never fade.
but also, how annoying is it going to be dragging that damn thing here and there with you? your walking speed will be severely limited by the rate at which those little roller balls can turn. annoying.
the biggest problem is dirt, though... can you imagine the *&^% that thing will pick when you're walking around outside, back and forth to school? not to mention the puddles you'll run into when it's raining... not to mention the snow you'll run into when the winter rolls around.
rollerpacks are stupid. move on.