Revealing mistake: When the Sergeant has the shotguns in the backpack on his back, and you see a close up of his face, you can see that the shotguns do not have triggers. On plastic prop rifles, the trigger is usually molded into the trigger guard in the pulled back position, and you can see this on these prop shotguns.
Other mistake: At the end, when Peter saves Mary Jane from the collapsing structure, he jumps up in the air and swings her to safety. However if you look at the web he is holding onto it is hanging down vertically. What did he attach the web to that was directly above him, the sky? Every bit of the structure around him was/had collapsed and the only thing remotely close to swing from was the cranes. Yet we see that was quite a distance away, so Peter would have had to shoot the web away from himself not above him. (01:47:50)
Continuity mistake: When Anakin attaches 3PO's right eye, one shot has the eye in his left hand, then the angle changes and the eye is being applied with the right hand. (00:37:20)
Continuity mistake: When Anakin is in the medical centre lying on his back being transformed into Darth Vader, you can see the main part of the mask being lowered into place but Anakin is not wearing the neck section of the mask that it connects to. We then see the main part lowering directly downwards, in the next shot the neck section is in place. (02:01:20)
Revealing mistake: When Ajax slams the hammer end of his spear into a man, he has his shield at his back. The top arrow in the shield is bent at a 90° angle and as Ajax moves the top (plastic) arrow droops down and the bottom arrow actually flops around. While still in the same location, when he sticks his spear into the sand and pulls the arrow out of his thigh, the arrows on his shield are gone. (00:42:20)
Revealing mistake: In the scene when Austin Powers goes to visit Dr. Evil in prison to ask about his father there is a shot of Dr. Evil with Austin's head partially in it. If you look at his reflection in the glass, you see he looks nothing like Austin. The person in the reflection is actually a body double. (00:21:20)
Visible crew/equipment: Watch for the boom when the cigar girl's Volvo boat swipes the building (it's on the top left of the screen on the widescreen version).
Deliberate mistake: Almost trivia, but not quite. When Mystique's looking through the guard files to find a suitable candidate, lots of photos flash up very quickly before she finds the guy she uses. Of note is that Bryan Singer pops up in guard uniform (with his own name), and so does someone called "Donner, L". This is most likely referring to Lauren Shuler Donner, one of the producers, and sex is specified as "F", but the photo is of a stubble-coated man. (00:23:10)
Deliberate mistake: When MIB agents exit the lift to get into the main hall of the MIB Office, the lift opens halfway up the wall and they need to go down a little platform. But when K and J return during the lockdown and face the trashcan with guns, the lift opens at floor level, so it can be conveniently peppered with bullets. (01:02:05)
Visible crew/equipment: Boom mic visible, reflected in Barb's motorbike helmet as she talks to Big Fatso.
Continuity mistake: During the scene where the police first go to arrest Howard and John is deciding which door is the right one his plastic face plate is down and in the next shot it is clearly up. (00:10:55)
Revealing mistake: During the bedroom scene with Felicity and Fat Bastard you can clearly see the air hose that fills his suit when he rolls over in the bed. (00:49:10)