This is what I have found:
"Plug and Touch uses the camera in the Nokia N8 to work out exactly what you’re up to. It takes photos at 10 frames per second, with the processor in the handset keeping an eye on you. If you stay in one place for a certain time – with your finger hovering for longer than 0.5 seconds, for instance, the phone works out that you’re trying to press a button. It’s also possible to scroll, and carry out other functions all via giant actions."

From here:http://www.noknok.tv/2010/09/16/noki...a-touchscreen/

Well it's one of the reasons that I would love to have my old n8 but it is not published.