Hmmm, not wild about the idea for several reasons:
1. They are bulky.
2. You'd need to stock several different sizes in hopes of having the right size on hand.
3. You'd need to encounter someone looking for diapers that had something you wanted. If they don't have diapers they probably don't have anything you'd want.
4. It takes a fair number of diapers to get a baby through the day, one or two would rarely be enough.
5. Karma.

However, they might be worth having on hand for good-will gifts.

Overall, I think there's a lot of better barter items out there.

-Blast, giving the opinion of a parent