If you preordered you have 24 hours to pick up the system, so the problem of skipping school to ensure your system isn't necessarily there. And if they happen to let go of your system early...well, in those cases you may have good luck being quite calm, asking for the manager, and discussing the issue with him and then further up the ladder if necessary (ie: manager doesn't care, sold your system and others regardless of preorder status, etc.).
If not, I would assume that a lot of people would tend to do what my brother did and hit local locations that are doing a Midnight Madness promo for the 360. As far as I know there's really no reason to be at those locations past 3 AM or so and, even if you were to rip open the box and play immediately, you still have a good two, three hours before school in most cases (assuming high school setting since college can do as far as five hours min. most of the time).
I just don't understand how skipping school is really even an issue. Most school districts will have the next day (Wednesday) off anyway or, failing that, Wednesday will end up being the typical "day before vacation" day where nothing actually happens. And if you really have to play that 360 the second you get it there's nothing wrong with an all-nighter, a bit of school, and if you really can't take the physical pressure you end up vomiting, passing out, hitting the nurse's office and getting carted home.
Man...the work ethic is dead.