I just got a Zojirushi NP-GD05 last week and already seem to have marks on the inside surface of the cooking bowl. It is not like they are deep gouges and I when I run my fingers over them it is hard to actually feel anything.
I am taking care to wash it with a sponge as opposed to a scouring pad. The only thing I can think of is that as I wash my rice (gently), the actual rice grains are marking the cooking bowl. However I thought the non-stick coating was supposed to be really hard wearing.