Steven Sinofsky published a new post on the Building Windows 8 blog, this time on landscape and portrait mode

A Windows 8 PC is really a new kind of device, one that scales from small, touch-only tablets to laptops and desktops. While reimagining Windows 8, we designed it to deliver a great experience regardless of the form factor or screen orientation. Tablet devices allow for ergonomic flexibility, allowing you to hold the device in whichever orientation is most comfortable to you and best suits your content.
One of the best things about a tablet is that you can hold it in your hands. It’s personal. Whether you’re reading the Sunday newspaper or browsing through a stack of wedding photos, being able to hold and touch what you interact with ties you emotionally to it. In the digital age, a lot of what is most important is on devices, so when planning Windows 8 we wanted to make sure that the experience could support any orientation that the device could be held in.
As we designed the end-to-end experience on different form factors in Windows 8, we used the following principles:

The experience tailors itself for all form factors: small screens, wide screens, laptops and desktops.
The experience takes advantage of widescreen formats for multi-tasking and for full-screen video.
The device can be held and interacted with in the way that is most comfortable.
Developers have the opportunity to create one app that runs on all views and orientations across form factors with minimal effort.

  Windows 8: Optimizing for both landscape and portrait