From a food perspective, it's a liability issue. Using that material in foodstuff's (specifically in beehives, which are mentioned in literature) is not approved by the FDA.
If you are eating the honey, it is no big deal at all.
If you are selling it and you have any assets that you treasure, you are putting them at some risk. The risk (or beekeeper assets) may be small enough as to not be a big deal to a given individual, but the risks do exist.
I am definitely no tree hugger, but it seems logical to me that putting something designed to kill termites into my coffee cup is probably not going to help me very much. Add to that the liability to my estate if I try to sell this coffee cup to another person and they begin to feel a bit queer and I don't mind putting a few coats of paint on the boxes.
The real point of this post is not so much to say that paint is better then wood preservative, but to say (especially to any new person reading this) that there are two sides to the coin, with regard to opinions on this matter. I'll leave it at that.