Continuity mistake: At the Unity Festival, when the Green Goblin flies past on the glider, the camera cuts to a shot of the balcony, and behind Harry and MJ there is a man in a black suit that takes a picture (you can see the flash from the camera). But when the camera cuts to a close up, the camera that was in his right hand has vanished and is now a glass of wine. (01:03:40)
Continuity mistake: When Spider-Man finishes beating up the thugs and after Mary Jane kisses Spider-Man, when you watch the one shot from the side, Mary Jane only starts to put his mask back on. But when the angle changes, Spider-Man's mask is properly on when Mary Jane didn't even move her hands. (01:21:40)
Continuity mistake: In the scene in Jameson's office after he throws his cigar out the window and the Goblin throws it back, when Jameson is looking at the cigar on his desk, he is sitting at an angle. Right before the Goblin crashes in, Jameson is sitting perfectly straight at the desk, with both hands on the desktop. (01:11:50)
Continuity mistake: In the Thanksgiving dinner scene, watch Mary Jane's arms after Norman asks Peter to repeat how he got hurt. When she is shown close up, her arms are folded. In the long shot, her hands are in her lap. They jump back and forth between the two positions. (01:24:50)
Visible crew/equipment: In the school fight scene where Peter beats Flash by punching him and making him collide against a teacher, his tray falls on his face. In that precise moment a camera with a hand on it can be briefly seen on the left side of the screen just a few moments before the shot points downwards.
Continuity mistake: In the scene where Osbourne tries the performance enhancers on himself, he takes off his labcoat and throws it into a corner. We see a long shot of the lab, and the coat is in at the base of the pillar. In a subsequent long shot however, the coat has moved a foot or so. (00:14:45)
Continuity mistake: During the scene in which Peter is introduced to Norman Osborn in front of the museum, keep an eye on the Volvo parked behind the Rolls Royce. When the camera first faces Mr. Osborn (Willem Dafoe), the Volvo in the background has the window rolled halfway down. Camera switches to Peter and Harry, then back to Mr. Osborn. This time the window is all the way up. When the camera comes back to Mr. Osborn again, there is someone leaning in the window talking to the driver. The next time the camera comes back to Mr. Osborn, the window is again halfway down. (00:05:54)
Continuity mistake: When Parker is chasing the robber into the abandoned warehouse, you see a shot of the robber holding the gun in his left hand and carrying the money bag in his right hand. However, the next shot you see him load a clip into the gun with the bag in his left hand and the gun in his right hand. (00:45:25)
Continuity mistake: When Mary Jane falls off the balcony she falls sideways except for a shot of her falling face down. Shot changes and she is falling sideways again.
Continuity mistake: When Flash is hit by the tray with food he raises his arms in disbelief. A shot later his arms are lowered and he repeats the previous movements.
Revealing mistake: When Osborn is gassed inside the vault and the doctor comes to aid him, 2 green squares are reflected on his glasses. The green fumes are already gone so it can't be that. Plus from the opposite angle there's no green wall anywhere, so it was the green screen used on the set or a continuity error when fumes were still on the set.
Suggested correction: I think it's the green smoke reflecting on his glasses. The chamber has rectangular windows so that's why the reflections are rectangular.
I don't think it's green screen, they look a bit small for that but there's something there, you are right. There're green little rectangles on his glasses even when he is doing CPR, when he is looking directly at Norman's face but no green stuff around Norman's head. Perhaps green smoke would be harmful or expensive, so they used regular white vapor and shone green lights on the smoke to make it appear green and later forgot to turn those lights off.
There are monitors with green colored animations throughout that scene, in fact we can see a monitor behind the doctor in the shared screenshot. It could be that the monitor is getting reflected on the glass walls of the chamber which then gets reflected on doctor's glasses.
Continuity mistake: When Peter wakes up the day after he was bitten by the spider and goes to the living room doing a little "stunt", Uncle Ben immediately turns to him, but in the next shot he makes a forward movement as Peter falls on the ground after the stunt.
Continuity mistake: When Peter tries his first web swinging on the rooftop, the sky turns from sunny to cloudy between shots.
