The EFBs i've come across so far are usually standard Windows XP pen tablets, however in my outfit we now operate the second military spec rugged platform of that kind. Main reason is that they hope to get lower repair and replacement bills than with our first platform (a standard HP tablet PC), main reason is that they have to withstand quite a wide range of different temperatures, vibration levels and shock from falling down, not to mention moisture. Since those things are now rugged PCs they are quite heavy and bad to handle in a cramped cockpit like the 737, so most of us are looking forward to the promised EFB II fixed installation where everything is fixed to the airplane and not manually handled by us. Documentation is allready only available in electronic form including the AFM, apparently a dual EFB-installation is quite enough to satisfy the regulator, dispatch with only one working EFB is approved, the EFB has to be stowed below 1000ft AGL.