As in, portrait not landscape. It’s the way to go. Which is to say, tablets should be held with the short bits at the top and bottom. And columns of text should be long-ish and narrow-ish. There are consequences, in particular for tablets.
Some evidence, were any needed:
Books, which when opened are somewhere between square and wider-than-tall, divide their text into two vertical rivers.
Newspapers. Already taller than wide, the text is still further sliced into tall-and-narrow.
The windows on your computer screen. Most screens live mostly in landscape mode, but many of your windows are tall-and-thin, and those that aren’t are often vertically sliced into panes.
Here’s the tablet conundrum: I find that full-size (i.e. iPad or Xoom scale) devices often sit most comfortably in the hand when held sideways. And, during a recent presentation I attended on app design for the tablet form factor, someone pointed out that a landscape-mode tablet, unlike a portrait-mode handset, recalls the shape of computer monitor; so presumably the user-experience lessons we’ve learned designing for monitors begin once again to apply.
Well, maybe. But what I foresee is a chance for overexuberant site designers to pack in marginalia and widgets and gadgets and social-media dung and so on ad nauseum. Thus requiring the services of things like Readability.
One solution on a tablet is to emulate book design and go two-column. But electric text wants to be scrolled, which doesn’t sit well with columnar layouts.
So hold your damn tablet the right way up. That’s the way the information wants to be, anyhow.