yield in C# doesn't work, not event the sample code?

I copied this code straight from reference: (http://unity3d.com/support/documentation/ScriptReference/index.Writing_Scripts_in_Csharp.html)

using UnityEngine; using System.Collections; public class PauseScript : MonoBehaviour { public void Awake() { Do(); print("This is printed immediately"); }

IEnumerator Do()
{
    print("Do now");
    yield return new WaitForSeconds(2);
    print("Do 2 seconds later");
}

}

I attached it to a cube prefrab and run it, mysteriously the line inside Do() never get executed... Then I tried the java version of the sample code, that worked fine...

Do (); print ("This is printed immediately");

function Do () { print("Do now");

yield WaitForSeconds (2);

print("Do 2 seconds later");

}

Could it be any setting in unity that I missed?? Any ideas??

Thanks guys..