Lynn pointed out earlier; ‘two handed interaction IS useful for many things‘. Bill Buxton has written a chapter on two handed input in his work in progress book on human input to computer systems. Here he states that the common view that human manual actions are generally unimanual is mistaken. Handwriting for instance is almost always seen as a one-handed activity, but in practice the non-dominant hand is used to hold the paper and as such forms a frame of reference. This bimanual task is asymmetric; the dominant hand is doing the precise work and the non-dominant hand frames the location. So I’ve been thinking how to implement two handed interaction.
Most examples I know which implement two handed touch interfaces use symmetrical actions. The left hand is doing the same as the right hand, or in case of the iPhone they are fingers of the same hand. I’m more interested in asymmetrical bimanual actions, preferably using physics. These mirror the natural way we use our hands in different tasks, or at least I hope so.
My initial brainstorm somewhere late at night gave me two possible implementations. Using you left hand to fix the object you are manipulating and the right hand to rotate it. This way you can rotate it around a different point than its centroid (lower action). This actions very much mirrors the two multi-touch rotation I disliked earlier 
. Another implementation is to use the left hand to hold the object and the right hand to scroll its content. (upper action). This action doesn’t have a very clear added value over more traditional approaches either, but it is a start. One benefit of this approach is that you can manipulate both the object and the content without the need of titlebars and scrollbars.
Two examples of asymmetrical bimanual touch gestures.
more to come…
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