Yeah, a lot here will tell you that it's normal, there was a similar thread over at Tactical Forums one day.
[url=http://64.177.53.248/ubb/Forum56/HTML/000497.html]AR15 deficiencies[/url]
That said, my Colt GM has A LOT of rounds through it and there is no wear on the buffer, none.
Some wear (not damage) can be considered normal since there may be a rough spot on the rear of the carrier. If it's not a rough, or high, spot on the carrier then often it's a mismatch (angular) between the upper and lower. In effect, the carrier is not coming directly to the rear compared to the bore line. When that happens one edge of the carrier contacts the buffer face first.
If you see dents arranged radially about the circumference of the buffer's face then you have trouble.
The wear/damage will always be radial bc the buffer spring rotates slightly with each compression.
[ed for speeling]