Well I for one regret David Miliband's decision to withdraw from frontline politics. Whatever one's political stance, it's always sad to see someone who is talented leave the scene. I understand why he has done it but it is a decision the Labour Party will come to regret.
I am not sure it will fulfill his aim of letting Ed Miliband get on with the job of leading the Labour Party in his own way. While David remains in Parliament his supporters will continue to press his case in the media and he will be seen as the King over the water. His every utterance will be pored over for signs of disloyalty to his brother.
As long as he sits on the backbenches there will be many of his acolytes who will believe that his day will still come.