One of the guys on my crew uses the split keyboard and he is a pro at it. It's pretty cool to watch him rapid fire out an email.
I haven't really tried to use the split keyboard. But I would think that after a while you would get really good at using it if you practiced enough. I don't like to type on the keyboard like that though. I think that I would be much faster typing like a tradition laptop keyboard. But whichever method is best for the user. I was wondering if Apple would implement some sort of swype keyboard to iOS. I think that that would assist those who haven't embraced the current software keyboard.