it's deep enough to take off part of the top layer and expose the oak coloured leather underneath.
this happened to my black cherry's as well, after just a few times. I really don't mind the scuffing though but I can see how one can find it annoying. This happened from regular wear.
on the other hand, I'm not using them over the summer - should I still condition them from time to time? I don't own any other shoes/boots that I need to "take care" of so I have no experience with this. Up to this point I've only applied mink oil 2 or 3 times over 4 months of wear. too much? too little?