I love to use my iPad with my computer. When doing work it's a calculator, notepad, every scientific PDF I own, another browser window, email. It goes under paper and notebooks, gets tossed around. In a very real way it's a computer window I've pulled out into meatspace. I kind of want another, though the price is too much for two.

My computer is almost exclusively emacs or maybe Illustrator/Photoshop.

In this sort of setup, the iPad shines for me.