DD had to be taught touch-typing with correct ergonomics, because her invented method was leading to evidence of repetitive stress injury. Her piano playing reflected a huge shift once we did that.
I'd heard the same thing-- that just letting them keyboard was the key. I don't know if that works well for some kids and not others, but it didn't work for our DD, that's all I know.
We used a combination of things to teach home row and basic skills, and then let her figure the rest out on her own. Her speed also improved DRAMATICALLY as we did this, so that was encouraging enough all on its own. She went from about 40wpm using her bizarro chicken-claw hunt and peck method to about 95 wpm using conventional touch-typing. That shift happened over the course of roughly one year, so it wasn't just maturation. At the same time, even increasing the amount of time she was spending on keyboarding didn't worsen her pain when keyboarding or playing the piano.
BBC-Mat-- tried, didn't really "click" for DD
Mavis Beacon-- booooooring, and DD didn't enjoy it
Typing Instructor for Kids (version 4 and later version 5 when we upgraded to windows 7)-- this was the most successful tool, at least in combination with the following things, which I'm going to recommend only with some serious misgivings/caveats--
WebKinz. {sigh} The verbal requirements were an unbelievably potent inducement to type well and fast-- and there was an embedded typing game, too, in the arcade style games.
Online Pokemon and other RPG-- again, this was a double-edged sword because of the time invested and the slyness with which she used it as an escape from other work that she found boring or unpleasant, but hey...
Coding
IM/Chat
Skype
Mileage may vary, but I mention those things because mostly I think that this is a matter of using your child's particular currency to leverage practice with the skills, and to see the NEED for the skills.
Good luck!!
