I learned how to type by trial and error on my mother's green Olivetti
typewriter, and after a few years of using computers, my four-fingered
technique served me well enough that I didn't think about learning how
to touch-type "properly".
Over the past few months, however, I've tried to use more fingers
efficiently, so that I don't have to move my hands as much. I adopted
the conventional finger positions for a week, found they didn't suit my
big hands (reaching non-alphanumeric keys on the keyboard was painful).
Now I've found a more comfortable position, and I can type accurately
and reasonably fast (though not as fast as before) without hurting my
hands.
Unfortunately, the price I paid was in losing the ability to fall back
to my earlier technique, and the loss of speed—though not an impediment
in practice—has rankled.
Today I discovered the perfect cure:
ztype
This is a "Space Invaders"-style game where you have to type falling
words to eliminate them before they reach you. It has a few annoying
bugs (sometimes the word you're typing is hidden behind others), but
it's extremely addictive nevertheless.