Upgrades will be tier-for-tier, with Vista Home Premium users getting to switch up to Windows 7 Home Premium when the time is right, Vista Business to Windows 7 Professional, and Vista Ultimate users getting an upgrade to Windows 7 Ultimate.
We tried it then and it couldn't have been easier, logging in while connected to your home network flips the switch based on IP address or MAC address, and then it worked at home or on the go, no password necessary.