I spent the first half of the game against Norwich sitting at the half-way line, about five rows back, on the same side as Evra. Because of all the stick he's been getting I paid particular attention to how much effort he was putting into getting back to defend when he was caught upfield. Every single time, without fail, he bust his balls to get back into position.
I think people don't appreciate the distance he covers in an average game. Because he likes (and is, by all accounts, encouraged) to get forwards so much he spends a lot of the game camped outside the opposition box. This means he has to do more running than almost any other player on the pitch. Stands to reason that he won't be able to do all this running at a full sprint.
It also means that if the opposition get hold of the ball and hoof it long to a striker who gets the ball under control and turns his marker (which happened repeatedly against Basle and few times against Norwich) Paddy would need a frigging moped to get back in time to help out our central defenders.