Depends on the device. How about this:

An extremely thin tablet that's essentially a touch screen connected to your home computer, aimed for use in the home. Tiny battery, very little computational power & storage, hooked up to your own beefy computer.

Edit - intended for use just in the home. I'd want one, certainly.

Too bad screens are using a good chunk of your device's battery. Reducing the radio and computation to close to zero may reduce consumption to 30-50% but it's not an order of magnitude. The batteries are here to stay I'm afraid - until we get some radically different display technology, along the lines of a color, 30 hertz e-ink.

This was more about having wireless power too (part of the parent comment). You don't need a 10 hour battery on something if you can power it wirelessly.

if pCell also enables wireless power, youd just need small buffer battery.

Well maybe sometimes, but given all the advantages of the envisaged connected approach, I'm not sure any more if the advantages of going off line will outweigh the disadvantages.

Do yourself a favor and get of town more. Leave the phone behind!

? I'm not sure I understand your point - I go out of town plenty, and I leave phone and computers behind. When I need phones or computers, I'm generally in or near urban areas.