In retrospect, Vader's whole plan to encase Luke in carbonite seems like a big waste of time:
Vader didn't even know if the carbon-freezing thing would even work safely on humans when he arrived on Bespin (Lando tells Vader that the procedure "might kill [Luke]"). He then goes through all the trouble to test it on Han Solo to make sure it is safe, despite continued protest from Lando and Fett.
So here is my question: why did Vader feel it necessary to have Luke encased in carbonite for the duration of his journey to the Emperor? Why not just put him in some max-security cell on his Super Star Destroyer instead?