The only game as far as I'm aware that properly makes use of it is Tearaway, but even then it only appears in a few places and was kind of awkward to control properly.
The Little Big Planet games use it too, in a more limited manner.
It is in fact awkward to use, IMO, and not just because of the software or Sony's implementation.
There are at least two big problems with it:
One is that it is really difficult to do Wacom-pen style hovering of a "cursor" on a capacitive surface with finger input in a way that works well universally for everyone without a lengthy and awkward calibration. And because of the non-direct method of interaction using your fingers on the back gives you, you really need some sort of non-action hovering indicator for this setup to work well.
The other is this: Put your hands in the positions shown in the original article. Now try moving your your index and middle fingers around as if touching the back surface of a device and try not to move your thumbs (and wrists) all over the place involuntarily. For most people this is difficult. When you are tightly gripping a device this becomes less of a problem but still contributes to the whole thing feeling very uncomfortable and unstable.
I'm nearly positive that various companies like Apple must have tested something like this out (either before/after the PS Vita) for a phone and just found it to be a poor solution when implemented in a real-world prototype.
The only game as far as I'm aware that properly makes use of it is Tearaway, but even then it only appears in a few places and was kind of awkward to control properly.