I usually think when writing. Think about what to write. I don't usually need to type faster and faster.
When I do type faster on a normal keyboard I make mistakes and I've got to go back and fix them (slowing me and my thoughts a lot).

I don't want to type 3 SMS in a minute or 4 emails in 30 secs.
I want to write a nice e-mail or a nice SMS that doesn't contain mistakes.