Change of Ownership cards in Maintenance Booklet
 

Any point in filling one of these out and mailing it to Porsche?

I sent mine in even though the car was seven years old when I bought it. They sent me a poster that was kind of nice.

I think in theory it is a good idea to let them know that you own the car. If there is a safety related recall they will have an easier time contacting you. They can probably track you down through your state division of motor vehicles, so I wouldn't lose any sleep over it.