My ears are fine without a tuning fork, so much so that I can tell you if a note is flat-ish or sharp-ish compared to 440 tuning. Not absolute to the Herz, but enough so that you can drive me mad by setting the transpose option on a keyboard and asking me to play it - my fingers get lost.
I used to play piano in a comedy act, and the venues often had worn down pianos - one time the piano was on the very edge of being a half step flat, to my ears. Kind of freaky. And there was the venue where they had two pianos, and the tuner had worked on the best one, but couldn't bring the pitch up far enough - so I had to use the bad one, which was closer. We always used to get comments about our rider - piano tuned at A=440 - but sometimes we came pretty close to having to cancel the show.
But it's funny how you can wring some nice music out of worn down, really old pianos, with a bit of effort. All those strings vibrating together, on an heavy cast iron frame, on aged wood - it works better than modern home pianos, the majority of which are hopelessly sterile. And keyboards are really no substitute.
