Surely the Kindle Fire is responsible for a lot of that, with a million sold per week, but it's generally agreed that the iPad is still holding its top of the hill position. And of course they are hardly interchangeable. [Update: Apple says they sold 15M iPads in the holiday quarter.)
But anyhoo, from zero to 19 percent in two years... And from 10 to 19 percent in two months! That's gotta be the fastest adoption rate of a new technology ever.
Oh, and by the way, according to other studies, the number one use of the Kindle Fire is: reading! I admit I would have hesitated to guess this. I think this is a good score for abstract thinking version sensual "thinking".
I am interested to see how reading will look in a mere ten years. What with thinner, lighter, cheaper ereaders, small and hopefully some bigger too for graphics-rich reading, and probably no turn of the rising trend of printing and distribution costs of paper publications, surely tablets and readers will by then have taken over a huge lump of reading duties in developed countries. And then (or well before), like with mobile phones, it may go even faster in less-developed countries, due to poor traditional infrastructure.