One of the new features for OEMs only that was released at the same time as MCE 2005 Update Rollup 2 is support for a new mode, called Away Mode.

How to describe it… It’s more ON than Suspend/Standby/S3, but less ON than ON. Not really a power saving mode as such. Needs a BIOS that supports it.

One of the Media Center PMs blogs about Away mode here.