I learned about this iPhone app from ZonalMarking.com's Twitter feed this morning, and it appears to be very interesting. It is called Total Football 2010 and it uses Opta data feeds to create graphical views of player and team performance in a match. The plan is to update the performance live during the match so that one can compare players and teams.
I have not yet loaded the app onto my iPhone, and it is more expensive than most apps, but I do plan on taking a look at it.
UPDATE: I downloaded the app this evening and checked out the analysis of some of the knockout matches from the 2006 World Cup. It is a very detailed graphical display of player performance in their offensive and defensive roles. I'm not sure that the way player influence is measured is the best way to determine that, but what I think would be the correct way is very computationally intensive.
Overall, I liked the app very much. It will definitely get used during the World Cup, and I encourage my readers with iPhones to check it out.