Like larez2 said, they should wear unevenly. Look at the back of a Boxster the next time you see one on the road and you'll see the camber is negative enough it's very noticeable.
I wouldn't pop the tires off and swap rims to rotate because then the negative camber will take your angled tire and it will be putting undue pressure on the edge that's thicker and now on the inside.
I started using bi-directional performance tires on the rear so they can be rotated without coming off the rims. Then the angle when they are rotated is correct. This helps me keep from having cupped tires and the road noise that comes with them. Combined with uni-directional tires on front, it gives me the performance I want and the 25-30K miles I like from a set of tires.
Get your tires balanced often (3K-5K miles max) since they can't go front to back. A cheap way to avoid excessive road noise and premature wear.
