Microsoft is trying their best to use the best available technology plus compatible with future technology with Windows 8. This is proven by the blog post in Building Windows 8, that discuss about supporting USB 3.0 in Windows 8.
How many times you gave up backing up larger files or transferring larger files because of the slow file transfer speed. With USB3 technology coming up with Windows 8 will able transfer files instantly. It is ten times faster than the USB2.0.
On the other hand Windows 8 USB3 technology will be having the biggest challenge to make it work with all the existing UBS devices. At this stage Windows 8 team is doing number of testing to make sure it will work smoothly with all the old and future devices.
Enjoy the small demonstration that shows how USB3.0 will change the way you transfer files between external devices.