Heavy callouses on your left hand will cause the keys to feel a little different sometimes--but you get used to it.
I would like to revive this discussion, as I'm thinking about picking up my guitar from the corner again. I used to play some guitar when I was a teenager and I got callous skin on the finger tips of my left hand only after a couple of days. At that time I didn't play so much piano, so I don't remember what the effects (if any) on the piano playing were. The hard skin disappeared quickly after i stopped playing.
So now two questions arise:
From a musical standpoint: Does it really feel just
different (but not worse) with callous skin, or does it make it more
difficult to control the touch? Would it be harder to work out the subtleties such as inner voices, based on the correct interpretation of the dynamics?
From a technical standpoint: Do more slips occur because of the callous skin when playing fast runs with the left hand (like for example in the revolutionary etude)?