Touchscreens and Ergonomics

With the release of Microsoft Windows 7 on the horizon and with one of it’s main features being that it supports a multitouch user-interface (similar to an iPhone or a Tablet PC), alongside an N-trig screen, it got me thinking about the potential usability and ergonomic issues that may arise.
Touchscreens are already in use on a few popular mainsteam systems, such as the HP TouchSmart and the Dell Lattitude XT. If, eventually, every computer has a touchscreen, what would the ergonomic implications be?
For PDAs and mobiles a touchscreen isn’t a problem, as they are designed to be carried and moving your hand to touch the screen is no different to touching the adjacent buttons. However, for desktop PCs, or even conventional laptops, it may prove a little more awkward. For starters, vertical touchscreens will force your arm/s to hang in the air instead of resting on a desk or a wrist rest. This would put immense pressure on your shoulders, arms and wrists throughout the day and could cause serious problems in the long term.
Simply putting touchscreens on conventional computers without altering their design is not practical, so new products would have to be designed to cater for this and existing products will eventually become redundant.
So, for all you budding product designers out there, get your thinking caps on. Maybe your product will feature on our site someday.