as a semi-tangent; your scenario exactly describes why I'm buying kindle books, and I don't even own an actual kindle.

I am remote programmer which needless to say puts me in different coffee shops throughout the city. I ride the bus multiple times a day.

I'm able to switch devices seamlessly as I trek around, and kindle updates my "last known reading location" - go Amazon.

Your scenario is harder but quite exponentially more valuable as we start to see more and more smart devices.