Several years ago, if you one who needed a portable the conventional wisdom was to buy the best possible desktop you could afford and the cheapest laptop you could get by with. Then, as laptops became more powerful, the general consensus changed to: buy the best possible laptop you can afford and hook it up to an external monitor. And now it seems the pendulum is swinging back to the dual-machine setup — people who were once MacBook Pro-only are going to MacBook Airs plus iMacs.