Yeah, i practice in the dark sometimes. Not much, but I do it. Most times I cover my hands or close my eyes to run my scales and play my basic chords in all inversions w/out looking. Next, I try to do some progressions
and maybe the blues scale in every key. It interesting to hear the sounds and chords when u can't see what u playing. I have got a keyboard in my mind so I play all the time w/out looking physically, but mentally i see where I am and what i want to play. Every now and then I look down for reassurance that I'm playing right.
I look at how blind play the piano, and I am amazed. It really takes a double helping of practice for them, but some of them sound better than people who have one or two eyes. I encourage everybody to practice w/out looking at your hands.