BETTER 3D MERGING
So in order for 3D objects to interact with each other they need to be merged into the same layer. Before CS5 you could only merge 3D objects of the same type. Like two primitive shapes or two 3D postcards. Well now you can merge any 3D shape with another. Just select them both and choose Merge 3D layers from the 3D menu. However, remember, you can still only merge two 3D layers at a time.