I started testing Windows 8 RTM in our domain environment and have found that the drive maps via Group Policy Preferences are not functioning if the "Reconnect" option is ticked. The drives are not mapped and there are no errors in the Event Log. If I untick the option, the drives map properly. These group policies function correctly with our Windows 7, Windows Vista and Windows XP clients.
This behavior occurs even when UAC is off.
Normally, when a drive map is applied via group policy preferences, event 1112 is generated in the System event log indicating that the drive map was successful, but that it won't be available until the next login. That is not happening here. It is as if the extension is just ignoring the directive.