Vastly faster, smoother, and lighter in both sound and video rendering whilst altogether being much more stable and vastly more power efficient? 

For people with new machines post June 2012 that registered? 
$15. Early October 2012

Developers and manufacturer?
Via MSDN. 1st of August 2012

For people with access to volume license re-sellers? 
 1st of September 2012

Final full general consumer retail price? 
Think the land of tulips for all general consumers, $40 


AAAAAAGHHHH!!!!?!?!!!!!!!!! !!!!?!? !!!!!! WINDOWS 8! FAST 'n' THINGS!!