I have a Vita, but the only game I've played that uses it is Tearaway. This game doesn't use it for precision navigation or selection, so it's hard to say how well a rear touchpad would work for that. Tearaway employs the rear touchpad for tapping to jump and pushing objects around. For that, it's surprisingly effective and adds a fun--if gimmicky--element to the gameplay. The Vita is quite a bit larger than most smartphones, and I could see problems with differing hand sizes requiring people to adjust their grips to use its entire surface--probably not as much of a problem on a phone. The Vita is played two-handed. I think a one-handed grip while using the rear touchpad on a smartphone would be more difficult as your finger's range of motion is limited. The OP article seems to anticipate this by focusing on small gestures rather than ones that would take your finger across a large surface.

On a tangent [Tearaway Spoiler Alert]...when beginning the game, Tearaway asks you to select your skin tone from a few presets. Knowing nothing about the game at that point, I thought that was really strange. I recall thinking, "I don't really care whether my character has my skin tone...and it's really odd that they'd presume that I would." But it turns out, that's not what the skin tone selection was for. In Tearaway, you use the rear touchpad to punch your fingers through the paper backdrops of the game to manipulate things. The first time I did this and they showed "my" fingers in the game, I was startled for a split second and then laughed out loud. Screenshot of the effect: http://media.officialplaystationmagazine.co.uk/files/2013/11...

It's more magical live as your virtual in-game fingers track the position and angle (angle presumably by extrapolating based upon the current finger position and average hand size/grip) of your actual fingers surprisingly well.