Don't know about Tim, but I've done it. I occasionally write short stories, and some of them hit that sort of length. (I'll be the first to admit they're not terribly good. Middling fan-fiction grade at best, but that has nothing to do with being written on my iPad, or even iPhone.) Most of the autocorrect issues I have come from unusual names, or made-up jargon in the stories.
The trick is that you don't need to thump the screen with your finger tips like you were taught to do with a normal keyboard. You don't need to press anything down, so lightly tapping the screen (such that your physical keyboard wouldn't be registering the presses) is sufficient, and helps you pick up any speed you might lose due to the change in feedback.
I type about 75 wpm on a good keyboard. I used to be faster, but most of my typing is C/C++ or C# these days, so I'm more used to reaching for strange punctuation than some of the 'normal' stuff.. Last time I tested on the iPad (almost a year ago), I hit just shy of 60 wpm.
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So don't "punch" the glass with your fingers. You don't need to press that hard. The amount of contact you need on the screen wouldn't even register on a standard, physical keyboard.
