Isn't it great how milk cartons fit all nice and snug in the fridge door? If you keep your milk there, you may want to stop. According to Good Housekeeping that is the worst place to put it.
Apparently the door is the warmest part of the fridge and is susceptible to temperature fluctuations. Items with natural preservatives such as condiments, jams and juices should be in the door.
They have other tips on food storage and the best way to organize your fridge here. Looks like I know what I'm doing this weekend.