Occasionally we do, but not for the typical scale (calcium) build up. Being on tank water here in Australia, which is rain water, we don't get a hard water scale that I grew up with and would literally litter the bottom of the kettle and could be tipped out of the coffee/tea mug/cup.
Periodically the inside of the kettle needs a clean to remove the build-up of eucalyptus leaf gum that is deposited from our rain water tanks. It's a brown residue that looks unsightly. Hard to explain and it's not that long since the kettle was last cleaned so it's only just beginning to build up again.
That will steadily get browner and browner until almost black...
Presumably there is something in the gum tree leaves that is water soluble and it certainly resembles the stagnant brown water with eucalyptus leaves in it, that find there way into everything. This is just the run off where the gutters need cleaning out on the shearing shed, but it is way too high to access easily, so we just live with it. Occasionally you'll get bits of dead eucalyptus leaves through the tap which is significantly better than one place we lived in in the UK where we'd get dead wasp parts coming through the taps...