Part of this will also depend on location/environment. I live in the high desert where the average humidity is about 20%, and have never had problems with rust, as long as I dry my knives after washing. I have a bigger problem with keeping the wood from drying out, though I prefer stabilized woods for less maintenance <--personal preference.
If you live with higher humidity, then you'll have to pay more attention, and it may be necessary to oil your knife at least some, if not, on a regular basis. Like sharpening, you'll understand more of what's going on by paying attention to the knives, and how they are reacting over time. Example, it's best not to store a knife for years without taking it out once in a while to check on it.