Earlier quoted context omitted.
That UX Sketchbook looks neat, but I wonder why no landscape orientation. Most people I know have the browser maximised and there are still a lot of laptops and desktops out there.
The limiting factor is reading habits, not browser size. Just because you can design in a landscape orientation doesn't mean you should and wider isn't necessarily better. It's not like magazines are 3 feet across because paper's cheap, right?
I do think the UX sketchbook is very neat - the squared paper inside the broswer frame is genius. It just seems perverse to only offer a single orientation in 2 different sizes. If it had portrait on one side and landscape on the other I'd buy it in a second (he hinted, in case the makers are reading).