Surface Book pre-orders sell out on Microsoft's site

People who want to buy Microsoft's new Surface Book laptop-tablet hybrid will have to look somewhere other than the company's online retail store, for the moment.The online Microsoft Store isn't letting people pre-order the new device. Instead it asks that they leave their email address so they can be notified when it's next available.Fortunately for Microsoft, this means that there's healthy demand for the machines. It's a positive sign that the Surface Book, which marks Microsoft's entry