There are two types of wear around the cam pin cutout. The type shown by zach in the first post is due to the cam pin head hitting the side of the receiver after the bolt unlocks. The type shown in QUIB's pics is due to wear between the carrier and receiver.
The second type of wear is completely normally and will eventually stop.
The first type of wear depends on the gas tube length, ammo type, index pin location on the barrel extension, index pin slot in the receiver, etc. Basically, depending on the above factors, the bolt may not fully turn the full extent (the cam pin won't move to the end of its slot in the carrier), before it unlocks from the barrel extension. This allows the cam pin head to contact the inside of the receiver. It has been my experience that this type of wear will eventually stop as well once the aluminum work hardens. However, its possible that the aluminum can extrude out into the charging handle channel causing the charging handle to get a little sticky. A little bit of filing will take care of that.