I would actually disagree with hand alternation as a goal. I think optimizing first for runs (see my other comment in this thread about runs for a description) would actually allow longer periods of relaxation. If you alternate hands each key press I have the feeling that you could actually decrease the opportunity for relaxation (in the case of a fast enough typist) because as soon as one hand is done you only have the time span of a single key press before it has to activate again. However, if you can type a run of 3-4 keys with a single hand using a single rotation of the wrist, and then alternate between left hand runs and right hand runs, I think you could allow even longer periods of relaxation than single-key alternation can give.