@rajeevk, we could compile from MSIL and not tell the developer. But you probably appreciate the chance to test out the app on your own the way your user will run it. After all, you'll want to profile it or maybe find that last on-device, optimized-only bug...
Reflection.Emit isn't allowed in the Windows Store profile so we haven't handled it in this go-around. Expression compile is supported and handled properly.