Update: the official Big Picture site is now live.
Valve has rolled out an official trailer for Steam's Big Picture Mode, effectively confirming reports that the new Steam user interface will be releasing/entering public beta tonight.
As we discussed earlier today, Big Picture Mode is designed to make Steam easy and intuitive to navigate on a widescreen television using an Xbox 360 controller; packing new menus, a radical virtual keyboard, an integrated web browser and new features. I could go on, but that magical moving picture (gosh, what an age we live in) aptly explains how the Steam experience has become a perfect fit for the living room.
Remind me: why do I own these consoles again? Facetiousness aside, we'll have some impressions for you soon - though you'll be able to try it out for yourself soon enough.