Continuity mistake: When Eduardo finds the letter on the mantlepiece about them apparently stealing the idea for Facebook and asks Mark if they did or not, he places a bottle on the mantlepiece just before he finds the letter. This bottle rotates slightly between shots without him touching it after placing it down. (00:49:15)
Continuity mistake: When Mark is filming them on the zip in the pool he is wet. After the doorbell rings you can see his bottom half is no longer wet, when he goes to answer the door.
Continuity mistake: When Sean shows up at the Palo Alto house Mark goes to the refrigerator and tosses Sean a beer. Right after this he tosses a beer to Sharon, Sean's friend. The bottle shatters on the wall and a few pieces get stuck in between the bricks. When the angle changes all of the pieces are instantly gone. A few seconds after this, right after Sean talks to the "wired in guy" the pieces are back. (01:19:50)
Continuity mistake: After Eduardo threatens Mark with legal action, part of Mark's computer keyboard previously smashed by Eduardo appears on the desk, when in the previous shot there was nothing there. (01:46:40 - 01:47:01)
Continuity mistake: When the twins are rowing we are shown a close up of them talking. After the scene ends the camera switches to a point where we are shown their backs and they are rowing towards us. Their rowing frequency changes between these two scenes. (00:17:40)