The only bad thing about this article is that sample sizes are incredibly hard to gauge value from when n<20. Really, only Ronaldo and I guess Cavani have large enough sample sizes.
There is a still a lot to be gathered from this from both the keeper's and goalie's end. I would like to see numbers on Franck Ribery. I remember Soccernomics raving about his randomness of taking pk's. He does not know where he will shoot it until the ball is kicked.