This is certainly a nice gesture from Warner, but I'll hang on to my HD DVDs. Since I greatly prefer the performance of my PS3 over that of my HD-A2, I generally only bought the HD DVD versions if they were better than the Blu-ray counterparts anyway. The only exceptions would be Casablanca and Batman Begins; one I got for free and the other has already been replaced, so I won't bother paying $12 just to get the identical BD.
Now if, say, Universal were to do something similar, I'd be tempted to trade up the Bourne flicks and the other releases they didn't bungle with DNR on Blu-ray.
"Out of the mists of history, the legendary Esquilax! A horse with the head of a rabbit... and the body... of a rabbit."