I too am obsessed with finding a way to make typing on the iPad live up to its full potential but I don't think this is the way. A physical overlay requiring precise positioning will destroy the fluid experience of the iPad which makes it so great. 

For instance when I'm typing a lot of text on my iPad I still often alternate between reading and writing. If I leave the overlay on when switching to read a blog post the very bottom of the page would always be obscured. It looks like trying to read through the plastic keys would be annoying at best and impossible at worst. On the other hand taking the overlay on and off would be a nuisance since you would need to get it into the exact right spot every time you wanted to start using it.

Instead if people want to type quickly on their iPad: Practice! Here is the typing test leaderboard for an app I made called TapTyping:

http://www.flairify.com/leaderboard/

The fastest typists have reached over 110 wpm with 98% accuracy (which is frickin' insane, BTW) but even speeds half of that are quite functional. I type at around 65 wpm on my iPad (85 on a keyboard) and I'm not shy at all about tapping out long passages of text when the inspiration hits me.

All of that said: these guys are helping to move the ball forward in touch screen input. I did indeed pledge $45.. Good luck!

Sent from my iPad