Fair point.  But I would point out that the only things this works with are things we have <i>thoroughly</i> mastered (e.g. walking).  People have issues talking and driving (e.g. in parts of Europe it's illegal to talk on a cell while driving because of all the accidents it causes).<p>In my experience it depends on the amount of processing required.  If I'm driving a straight away with traffic going mostly the same speed I can hold complex conversations.  As soon as something happens on the road I drop the conversation until my attention isn't needed on the road anymore.