Continuity mistake: When Mary Jane halts the cab, there's a couple walking behind her, who disappear in the close-up of her opening the door.
Continuity mistake: Down in the sewer, the wad of dollar bills moves away from the puddle between the close and wide angles.
Continuity mistake: Before Harry throws the bomb at Evil Peter, two bombs can be seen together next to the place where he is lying. Half a second later, when Harry picks up one of them, the grenades are apart from each other.
Continuity mistake: Reporter Jennifer Dugan's fringe swaps from right to left between the moment when she is reporting about Sandman, Venom and Spidey's fight and the moment when she appears on the news one frame later. (01:53:25)
Continuity mistake: The first time Peter is out and about as black Spidey, Eddie Brock runs up behind him and raises his camera. We then cut instantly to a shot of just Eddie, and he no longer has his camera raised, with no time to move it between shots.
Continuity mistake: Eddie exits the cab and runs towards Black Spidey. From a low shot Eddie's legs slow down and walk really slowly towards him. Then from a close-up of him he is seen running again and then stopping.
Continuity mistake: When Peter lands on the cab, MJ has her fringe all messed up and says "Peter, we'll both die". angle on Spidey, and when back to MJ she's perfectly combed and neat looking.
Continuity mistake: When Sandman leaves his ex wife and daughter, the daughter's position swaps from standing in the middle of a corridor to laying very close to a wall.
Continuity mistake: At the end of the final battle involving all 4 superheroes, Sandman destroys the building's iron structure with a blast of his hand, but in further shots it appears undamaged.
Continuity mistake: When Peter first goes to see Aunt May and tells her he's going to ask her to marry him, Aunt May in the first shot goes to hug Peter on his left shoulder, it cuts away and in the following shot she has hugged Peter on his right shoulder so that the camera can see Peter's face.
Continuity mistake: When the steel beam is sweeping the floor underneath the destroyed office, the model in pink disappears from the wide angle.
Continuity mistake: When the office floor collapses, Gwen and a girl in green are struggling not to fall down. In a close-up, one second later, the girl is replaced by a chair. She can be seen several meters away, next to a guy who magically appeared on scene.
Continuity mistake: During the "Keys to the City" ceremony, when people are chanting for Gwen Stacy to kiss Spider-Man, some of the same extras can be seen standing among different people in the crowd, in successive shots.
Continuity mistake: When the steel beam destroys the office, it breaks a window and a pillar. From the outside, the pillar is intact.
Continuity mistake: In the bell tower, when the slimy thing falls on Eddie, he covers himself with both hands. In the close-up his hands are down and raises just one of them.
Continuity mistake: When Peter is thrown against a brick wall, he produces a big hole around his left shoulder. In the close-up the hole is smaller.
Continuity mistake: Peter opens his shirt wide to see his evil Spidey suit underneath. When the angle changes, a frame later to a close-up of his neck and face, his shirt is closed.
Continuity mistake: Before the cop climbs on the truck, he shields himself on the truck's cabin and you can easily notice the tarp is perfectly tied by a dozen strings. When he climbs up, all the knots magically untie and he manages to pull the tarp away. His buddy couldn't have done it because he always appears with the gun in his hand, covering him.
Continuity mistake: When Jameson kicks out one of his employees from his office for coming up with another stupid idea, Brock sneaks in through the door into his office, but if you look at the black guy in the office he is holding a piece of paper in his right hand and his other hand is in his pocket, yet in the following shot from inside the office, the black guy is now holding the piece of paper with both hands.
Continuity mistake: The Bank truck full stops away from a zebra crossing, but the close shot shows it on top of it.
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