Cam lobes worn around the edges

Just took off the valve cover to check up on my clearances (checked and shimmed valves for the first time about six months ago). Now that I'm a little more familiar with what I'm looking at and dealing with, I noticed that some of the cams are worn heavily around their edges. And I mean... there are obvious shavings of metal missing.

Valve clearances are all in spec right now. If anything, a few are a little on the loose side. I don't think the PO ever checked the clearances as they were almost all really tight when I first shimmed them. I think I swapped or replaced a shim on almost every single valve.

First off, I know that this ISN'T a good thing.

Any ideas as to the cause? And how severe are my potential problems here by continuing to run on these cams?

 

Post a pic of them. Some cams have leftovers from the casting and and machening process that may look like that but are prefectly good cams. If there is something wrong you will also see marks on the valve shims.