I found this to be true. I typed Dvorak for a few years while in University, but switched back to QWERTY when I entered the workforce. I was pleasantly surprised that the increased speed and comfort I had attributed to Dvorak was maintained when I went back to QWERTY. It may have been less efficient than putting the same time I to traditional typing training would have been, but it definitely did increase my general skills as a typist to practice a new layout "from scratch".