Technique 5: Advanced shadow techniques
Besides simple projection, you still have many ways to give an object a three-dimensional sense. A long shadow can greatly change the spatial relationship between the object and its shadow.
In the following example, a same coke can is given a different shadow and darkness, and it results different overall effect.

Examples on the Web

Emotions by Mike: clever use of a shadow (and light), which has converted the flat surface into a floor.

Superkix: Using project to keep the sports shoes floating on the top of the page. When you zoom the page, the shadow will move along, as if the source of light is moving at the same time.

Edited By Dan Li