He ruined Tim Henman's serve the same way. It went from being a good if a bit erratic serve, to a less erratic one which never got any free points and was easily attackable.
That was a disaster, Tim was a sitting duck when he approached the net on many occasions. Tim should have been in his prime, as soon as he left that loon he won Paris Masters and had his wonderful 2004. Apparently the change in serve also nearly destroyed his shoulder.
However I do think Roddicks pre 2006 power game would not work today so he had the right idea by trying to change it. Roddick is pretty old now, but then again so is Ferrer and Federer.