Tablets and GPS units should be legal to use during driving. What is illegal is if the device is a
two way communication device for
text or voice or
video such as DVD TV etc.
Here are Oregon's laws, YMMV with other states:
http://www.oregonlaws.org/ors/811.507
http://www.oregonlaws.org/ors/815.240
What is also in question is windshield mounting (suction cups) which are illegal in many states:
http://www.poi-factory.com/node/34521
but when I go to the actual Oregon statute, it is really about
not obstructing the windshield view:
http://www.oregonlaws.org/ors/815.220
So my conclusion is that you can use a tablet for navigation and music services while driving, but it should not block your view.
DryVah's installation is perfect, it is what you see in many police cruisers with laptops (and you know they comply!).
Here's my installation on a smaller tablet on my old VW, it is a dashtop mount, but as you can see, it really doesn't impair the visibility looking ahead. It looks as if the view impaired at the bottom of the windshield view a bit, I didn't take the photo in the driver's seat from eye point of view:
The mount (black material) is by
www.proclipusa.com (aka Brodit in UK/Europe) and very good quality. ProClip mounts have the provision to have a charge port built in, so the tablet charges when you drive. They make mounts for almost every tablet and laptop out there. The aluminum base is homemade.