Visible crew/equipment: When El Wray and the police arrive at the hospital as Dakota drives off, at the very back of the shot is the crane used for the lighting (confirmed on audio commentary).
Revealing mistake: When the zombies are eating the intern in the hospital, you can see one of his ribs move as if it were made out of rubber. (00:51:20)
Other mistake: When Wray goes to save Cherry from the hospital, he puts on latex gloves to stab the infected. But after he gets Cherry, he stabs a zombie with his bare hands. (00:51:15 - 00:53:25)
Visible crew/equipment: In the very first scene of the movie when we see Rose McGowan dance, the whole film crew is visible in the mirrors behind the stage she's dancing on.