Got to sit a Model S Beta model with my Maui Jims this morning. The good news is that the view through these polarized sunglasses was very nice - way better than looking at my iPhone 3GS, for instance.
The video below shows how tilting your head affects how much light gets through. Interestingly, the Dashboard screen wasn't symmetric. 45 degrees to the right and the screen is completely dark. But, you can go past 90 to the left without affecting brightness much.