Hi Stampy,
the power off function already exists on the remote, you can set it to close videobox, or to completely shut down Windows - I will have a look exactly were in the settings menu it is but the option exists.
also some computers also have the option in the BIOS to automatically power on when the power is switched on, so say they power down and then turn off at the plug, the next time they turn the plug back on the system will automatically turn on.
Also agreed that a easy way to reset the credits back to 0 would be great, I was thinking of looking into this to try and find where it stores the credit info, that way a little script could be written to reset it every time the PC loads up.