I usually don't worry too much about my carbon knives, I just wipe em off after I'm done. If I have been cutting something acidic, I'll rinse em off or at least wipe em with a moist rag.
The only time I've had a problem is when I am really sweaty, I had my white owl on me at the gym once and although I didn't use the knife to cut anything, I did work up a good sweat and I didn't wipe the knife off, a couple days later I found spotting over a large portion of the blade. I caught it fast enough that a quick scrubbing with some 0000 steel wool and WD40 got rid of all the active rust, the spots are still visible, but it really doesn't make a difference to me, they'll go away pretty quickly if I cut up some apples.