Continuity mistake: When Spiderman lands Gwen and leaves, from the back shots her hair stirs violently because of the wind. From the front, it is nicely combed and the wind is not as strong.
Continuity mistake: In the shot just after Green Goblin is done dispersing both the super villains and offers his hand to help Spider-Man up, watch Green Goblin's face closely when he is first shown from a distance, when his face mask has just rolled up. The right side of his face, which is supposedly disfigured (due to his earlier fight with Peter in his flat), looks normal and smooth. Then in the following shot (after the camera goes back on to Green Goblin from Spider-Man lying down looking at him) when the camera shows Green Goblin from close (while Spider-Man slowly gets up at the forefront), his face is shown disfigured again.
Continuity mistake: The Hawaiian doll on the hanging cab moves around between the first and second shot.
Continuity mistake: When the two models stare at the steel beam, there's an employee sitting next to the model with the green shirt. In the wide angle he dissapears. If he had run away he would've been seen because he was standing very close to her.
Continuity mistake: Close to the middle of the film when Harry returns to his mansion with Peter, the butler hugs him on his left shoulder yet when the shot changes he's hugged him on his right, this is so you can see Harry's (James Franco) face not the butler's.
Continuity mistake: When Peter's looking at himself in the mirror in his apartment after yelling at the landlord, his hair's down in the first shot we see of him, but swept to one side when we see the reflection.
Continuity mistake: At the jazz bar, the amount of people by the bar and their positions (close together/apart, seated/standing up) is inconsistent in every single shot.
Continuity mistake: During the whole Harry-in-the hopsital scene the tube on his chest keeps changing positions all the time.
Continuity mistake: About to kill Venom, when Spidey is straining to break the web around his wrists, a fringe of hair falls on his face. A shot later his hair is combed and looks hair-dried.
Continuity mistake: In the scene where Brock is in Jameson's office showing him the picture of Spider-Man, Peter walks in and hands Jameson a picture, in this shot we can see Brock looking at the picture of what Peter took, and in the following shot Brock is looking directly at Peter asking him "how did he get that high".
Continuity mistake: When Peter is reanimating Osborn, Harry's head keeps swapping form looking upwards, sideways, slightly tilted. between shots. Peter's movements are not that brusque to produce the changes.
Continuity mistake: From the truck, Sandman boosts some cars away. One of them goes zooming straight against a corner on the left side of the street. When the angle changes, not only has the car changed positions to the center of the street, but a man and a car appear perfectly intact and calmed on the same spot where the car was before.
Continuity mistake: When Peter visits Harry at the hospital, Harry says: "The doctor says I had an accident". then he turns his head to the right, facing upwards. In the immediate angle he is still facing left.
Continuity mistake: When Sandman is down in the sewer, the stack of dollar bills on the right has no plastic wrap around. When the angle changes its green colour has faded and you can notice plastic securing the wads.
Continuity mistake: During the crane incident scene when Gwen is holding onto the telephone you can see her sliding down the damaged office floor with her legs almost over the edge, yet in the following shot when the phone's cord snaps, she is a lot further up the office floor and slides down again to the edge.
Continuity mistake: In the scene that Harry yells to Bernard (his butler) to get food because they are having a guest, the first shot of Bernard shows a small table with a vase of white flowers on it. In subsequent shots of the butler within this scene, the flowers are no longer on the table.
Continuity mistake: When the steel beam first crashes, Gwen lays very close to the side where it strikes. From the outside, she has moved way to the opposite side.
Continuity mistake: When Gwen is sliding down the office floor, she is facing upwards. Half a second later she is facing downwards.
Continuity mistake: When Peter and MJ are on the web, after he says "I always loved you" she smiles and shows a thick and long strand of hair along her forehead. Half a second later the face is spotless.
Continuity mistake: When Peter exits the theater, a woman with a bouquet of flowers disappears in the wide shot.
Chosen answer: Answered in the comics: Peter's Spider-Sense tells him if someone is looking when he's about to enter/exit the apartment as Spider-Man.
Captain Defenestrator