Following the session I had the pleasure of hosting at TechDays 2011 in Geneva, you will find here all the sources of the demonstration project as a Visual Studio 2010 and some explanation of this one. Links to the powerpoint and the video of the session are also recalled.
With the JSON Binding Support in MVC 3, you can send JSON encoded data to the actions and the model will be automatically bound to parameters. This allows the connection between server and client data by sending and receiving JSON those above.
The IValidatableObject interface introduced with version 4 of .NET framework is supported by MVC 3. It allows a level validation of the model and allows you to return specific messages about the state of the model.