Are two screen devices better than one?

A lot of 2 screen tablets and laptops are coming up in the market. We have seen one of them: #-Link-Snipped-#and then there is Acer Iconica 6120 and so on..

The principle behind bringing out 2 screen devices must be ease of interchangeability of applications. If you have only one application visible at a time, you must constantly take a second or two to switch the display from one application to another. Instead use 2 screens with 2 applications running simultaneously.

What do you think about it?