A common scenario that seems underdocumented to me in the latest MVC release, is how does one use RedirectToAction while passing a value to that action?

In the December CTP, you would do this:

RedirectToAction( new{
     controller = "Blah",
     action = "Blah",
     foo = "Bar"
} );

The new syntax is close, but not easily discoverable. Instead of the above, from now on you should use:

RedirectToAction( new RouteValueDictionary(
     new{
          controller = "Blah",
          action = "Blah",
          foo = "Bar"
     }
));