I was never taught how to type... I'm fast enough, 120-140wpm depending on the keyboard and what I'm typing. I think the speed came from playing online games and needing to communicate quickly before suffering the consequences of not controlling my character.
The end result is that I have a strange typing pattern and I use the "wrong" fingers for keys.
I share this experience and my typing on a normal keyboard is still only using a few fingers and moving them around all over the place. On a split keyboard even, i still 'misplace' some fingers because my pinky finger is so short i can't hit 'p' key comfortably with it.
Still, I think having a split keyboard has overall been a benefit to my typing experience and type faster on it than I could on a normal keyboard.
The end result is that I have a strange typing pattern and I use the "wrong" fingers for keys.