Personally I would go for single device that does everything I need. Something on the lines of what Ubuntu is doing. Even Surface to an extent solves this issue. I don't want to carry an iPhone to call/msg/listen to music, an iPad to casually use internet/read/play games and a laptop for everything else. Better carry one phone which does call/msg/music/internet,reading and minor editing/office stuffs when plugged to dock.
After owning an iPad mini I have to say that an as-light-as-possible 7'' tablet appears to be one more device that's very useful have / bring along. It allows you reading / media consumption on a device with a satisfying screen size that's as light as a medium paperback book, i.e. you can hold it for extended periods without getting tired.
