Formula One drivers are famously compact little guys and tall drivers are definitely in the minority. At six feet tall, Nico Hulkenberg is one of the taller ones. That means he has bigger feet. And those big feet seem to be too large for his new car.
F1 designers are always working to make things more compact in the name of mechanical and aerodynamic efficiency. The nose and end of the monocoque is one area that receives a lot of attention in order to be as compact as is allowed by the rules. This makes the car a tight squeeze for the drivers.
The 2013 Sauber C32, which is impressing other teams in the paddock, has a very tight nose and pedal box that can't be modified. Nico Hulkenberg has large feet which also cannot really be modified. The result is that Hulk is finding it difficult to get on the gas and brake at the same time. This is a bad thing.
Sauber's solution is to cut down Hulk's shoes in order to let his feet fit properly in the car. It should end up being all ok for Nico. He might just be a little less comfortable when he's walking around the paddock.