Source: http://static.tvtropes.org/pmwiki/pub/images/TV_Tropes_Flash...
Also, I think this generally would confuse users. I visit at 10AM it looks one way, I visit at 3PM it looks another, and I have no idea why as a user. Even if you paired it with other elements, you've still got the shadow all over the place.
I remember about 10 years ago watching a guy in school build a site that had a header that would have full sunrise-sunset based on your time in cute artwork. If you gave your location, it would display current weather too.
So OP, I think this has limited use; but its good to explore and experiment and see what you end up with. Perhaps with more thought/iterations you'll end up with something really amazing.
I'm not being argumentative; there is a history of the "desktop" metaphor, where it did seem sort of like the user was looking down on it from above. That particular approach to the metaphor seems to have faded deep into history. Not saying it's wrong, just that we seem to have moved somewhere else with UI, and I feel like a corkboard with pieces of paper tacked to it is a more fitting analogy for the way many of our current desktops work. The way shadows are used in most current desktops match that metaphor more closely than objects on a horizontal "desk" surface. And, given that we never use screens sitting flat on a horizontal surface (even the Microsoft Surface evolved to go vertical). The ergonomics of staring straight down is pretty awful. Our heads get really heavy at that angle, causing back pain.
Edit: Some "desktop" metaphor UIs where a "top-down" light source might logically lead to OPs shadow design:
http://blog.codinghorror.com/content/images/uploads/2006/05/...
http://kruzeniski.com/wp-content/uploads/2011/04/how_print_i...
Even the modern take (Bumptop for Mac) seems needlessly cluttered and cumbersome to manage. Then again, I prefer tiled interfaces, so I lean toward the extreme on the other end of the spectrum.