@Bass: just for the sake of argument:
1 legal pad only contains 50 sheets. A tablet has several GB of storage that are good for 1 bajillion pages. 1 bajillion / 50 * 0.50$ = 1 bajillion cents. Tablet is way cheaper.
Battery life: some tablets (notably the iPad) claim 9-10 hours, and you can actually recharge the thing. But that doesn't matter much as your carpal tunnel will probably sue long before that anyway.
Never thought about the toilet paper angle... I must admit that a slate won't do you much good in that scenario, but the word "papercut" comes to mind, with a disturbing new twist.
I guess tablets win. Go digital!