In case any of you haven't checked out lostepedia about the magic box, there's a lot of REALLY good thoughts here :

Magic box/Theories - Lostpedia

The only other thought I can think of is that maybe the magic box is related somehow to Pandora's Box - that all it contains is evil. This might mean that what Locke desires will never turn out to be anything good for him, revenge on Anthony Cooper won't make him any happier. It may perhaps be this way only for the "flawed" ones who aren't on the list, that when they come into contact with the box they manifest something terrible, whereas the unflawed people truly get their desires. It also might mean that the box can only be used once by any single person, which would explain why Henry couldn't magic up another submarine.

Cindy and the kids certainly looked very happy, maybe they got their desires?