As I understand it, the "friction" induced in your finger is purely a sensation. I mean how much force can it actually apply to your finger?

Also, the actual nature of the surface isn't altered - I wonder if you have two sensations at once?

Personally, I've been waiting for this for a long time... touch-typing on a screen (as it is common today, iphones and androids being ubiquitous) sucks, as you mistype regularly, even as you look at your screen.