Don't quote me on this but I believe there is already a 2008 map update out, however, I understand another is due and will be an 05/2008 (May 2008) DVD update for PCM 2 ('05 models onwards) and above.
Porsche have conveniently changed the part number for the DVD navigation update. Therefore there is no way to tell if the current MAP is actually an update on previous. As far as I'm aware the last update was MAY 2007. Even the dealers are unable to tell you if the current new part number is actually an update on previous as the new part number is a package including update Cd's for the PCM to fix various bugs. As to adding data to the map DVD you would need to uncompile the code , understand the GPS co ordinates ofd speed cameras then recompile and burn the data. That's a complete waste of anyones time , even if it could be done. Better and more up to date to buy a roadangel or inforad unit for about 50 pounds and install below the heating controls. These will tell you all you need to know and can be updated much easier.