For something you need to hold with both hands(which I assume how you use your iPad), I think the landscape orientation is more natural and comfortable. That's how we hold a book while reading lying down.
The vast majority of books are taller than they are high. It’s way more natural to read books on the iPad in portrait orientation, and that’s also how it’s shown in iPad commercials[1].
When you open a book (which is the only way you can read it!), it is definitely wider than it is tall. And hence I find it much more natural to hold a tablet in the landscape mode.
Samuel_Michon|12 years ago
[1] http://www.youtube.com/watch?v=bhC40QCZML0
jonas_maj|12 years ago