Earlier quoted context omitted.
We already have setups that can accurately determine where you will be looking a fraction of a second in the future. Do you have a link to more information about this? That's really impressive.
One's saccade eye movements are very regular in acceleration profile, so it's possible to determine where you're going to look from the start of the saccade movement. I could not find the original reference, but there is some highly technical information here: http://books.google.com/books?id=27jCNmafYU4C&pg=PA150&#...
http://www.denverpost.com/recommended/ci_20768271
And it only takes common sense to realize that we don't look at every key we type, and it makes it faster. The quickest typists don't have to look at the keyboard at all, and this increases efficiency. Both handwriting and eye tracking are much much slower than typing, no matter what. You can be the fastest handwriter on the planet, and still a moderately talented typist will burn the shit out of you. It just takes less time to hit a key than it does to write an entire letter form.
I realize my first comment was kind of mean and sarcastic, but that was because this idea is so completely stupid and not progressive at all that I thought the relatively intelligent community on hacker news would realize this immediately. All my friends and co-workers who saw it were like "this is completely dumb"... immediately.
I understand that people like things that are 'different' and 'progressive', but this particular tool is neither of the above. It's a fun little trick that is totally not practically useful in any way.