They should wear unevenly if they are are aligned properly.
http://www.986faq.com/2-0/default.asp:
"The Boxster has negative camber on its wheels. This means that the tops of the wheels slant in toward the middle of the car. This negative camber will result in more wear on the inside edges of your tires than on the outside."
I wouldn't rotate them, but that's just me.
HTH,
Larez