CONFIRMED: XBOX 360 Backwards Compatible
Engadget confirms that Xbox 360 will be backwards compatible with most Xbox 1 games.
I will definitely be pre-ordering the new Xbox when it is available. I think it's given me enough impetus to build myself a decent Media Center PC. I really wish the new Tablet I'm getting could have Media Center & Tablet combined, but I remember BillG saying that they will probably offer that SKU for Longhorn.