My understanding is that linked duplicates share an object's material properties and mesh data, but not its object transform properties. In a scene I am working on, I very much like the efficiency of having the mesh data being shared while also being able to scale and rotate instances. But I need to be able to assign a different image texture to each instance sharing the mesh's UV map (which comprises only a small portion of the mesh). If there is no way to make an actual linked duplicate do this, is there some other approach that will keep the mesh data linked?
By default a material slot is linked to ObjectData (and then a material is added to the slot). In your case change it so that the material slot is linked to the Object and then add/assign a material.
You can have some material slots that link materials to ObjectData and when needed link to Object. So your objects are still using the same mesh (not duplicating it) but only duplicating material for chosen material slots.
Note: The defaults can be customized from the User Preferences Editor's ''Editing'' tab. Under ''Link Materials To'' section choose Object and save settings as default.