Coming out of talk on Silverlight and XNA (remember, devs can now combine both, making regular apps with 3D, immersive graphics), an interesting question was brought up: Can developers mix Silverlight and XNA on Windows or Xbox? Answer: no, they cannot.
Microsoft does not have any tools for devs nor anything to announce on the matter, though they have built the Windows Phone tools with Windows and Xbox programming in mind, but as of now, there seems to be no immediate plans to bring over that functionality. What's interesting is this technically breaks the much touted "3 screens" model whereby devs can write roughly 80% of the app and have it compatible with the PC, Xbox and Windows Phones. Now, with the addition of Silverlight to games (and devs do like that ability), this is not the case anymore.
Will it have a big impact? Too early to tell and certainly Microsoft can port over this feature to PC and Xbox in the future. But for now, devs will technically be breaking that ability if they use both languages in the same app or game.
Anyways, for fun though, watch the top vid to see some more XNA + Silverlight combos. The first part shows how video can now be manipulated dynamically, making it like a liquid to the touch...very cool (the audience clapped after this) and the second shows a demo augmented reality app with 3D graphics "floating". The ability to add XNA graphics to the camera can result in some really cool 3D effects.