Some have asked for more detail on Away Mode and what it does:

Away Mode does the following when invoked:

• Shuts down the video signal at the port
• Mutes all system audio
• Blocks HID and PS/2 input devices (so your cat does not walk across the “delete” key and delete your library)
• Puts the CPU into “adaptive” mode, which may save power depending on what’s running
• Notifies kernel-mode and user-mode components of the transition (enables HW like video cards to clock-down or front-panel displays to change content, enables SW to do “smart” things like IM going to “away”)
• Notifies the BIOS through an ACPI control method of the transition (enables the power LED to change from green to whatever, enables a different thermal profile to be put in place if the OEM decides)
• Wakes back up when flash devices (USB FOB, flash card) are inserted
• Wakes back up when an optical disc is inserted in the drive

The intention here is to provide a “user not present” state to the machine so you can walk away, know that your recording is going to happen (or not be interrupted) while not badgering the user with a screen, audio, etc.  It is *not* intended to be a power management state. Today, this is the only way to ensure that your media center extender will always work w/o having to worry if your MCE host is turned on or not.  Also is great in that the system does not have to wake from S3 to record – and become noisy in the process.

To be clear though - Away Mode is only offered with new PCs. Maybe not popular at the moment, but the best way to make sure that Away Mode machines work as advertised.