A demonstration shown at TechEd Middle East shows just how the cross platform integration is expected to work with the newly announced Windows Phone 7 Series along with Xbox and Windows. The announcement that this type of integration was coming dates back to 2006 so it is nice to see it come to fruition.
The nicest part of the demonstration is that the game will run across all three platforms and apparently about 90% of the code is the same across all three platforms. The remaining 10% is only required to make sure it runs on the unique platform it will be played on. Of course this comes with the needed support of Xbox controller, phone touchscreen or keyboard and mouse for Windows. The cross platform ability also includes a one save policy meaning you could stop playing a game on the Xbox, pick it up on the way to work and then come home and finish it on your Windows PC. Very cool.
I have attached the video showing Indiana Jones which takes advantage of this technology.