After the update the other duplication glitch may not be working for you, but this video http://www.youtube.com/watch?v=Ns5IXECJUzc shows you that you can still dupe, but using a different technique!

1. Place down dispenser.
2. Begin destroying it with a pick axe.
3. Just before it is about to be totally destroyed, switch to something else.
4. Open the dispenser.
5. Drag and drop the item in the center slot.
6. Hold down A on the item.
7. Drop the item you used to do the duplication and then you can pick up the dupes!