Visible crew/equipment: During the "target acquired" chase scene when the red pickup truck flips over after going through the split semi-trailer there is an overhead shot shown of the action. The next shot when the T-X looks in her rear view mirror at the action, the camera crane that filmed the previous overhead shot is visible in the background. (00:32:25)
Continuity mistake: When the T-800 first drives the truck into the Vet clinic, the truck has crashed into the building, so that the doors are inside the clinic. Yet in the very next shot when he gets out, the truck has moved back so that the doors can open cleanly, without the T-800 backing the truck up. Then when John escapes the cage and he runs into the T-800, you can see the truck inside the clinic. It is now more than halfway inside the building. (00:24:15)
Continuity mistake: When the Terminator is hitting the T-X with the fire extinguisher, she puts her fist up and punctures it so the Terminator chucks it down on the floor. We see it on the floor again, but when the Terminator is running towards the T-X you see where the extinguisher was but now it has vanished. (01:18:55)
Continuity mistake: During the shooting scene at the cemetery, note one of the stones (rectangular from the left) behind T-101 when he comes out carrying a coffin. You can see it has 5 holes - 3 left, 2 upper right side. However, a few seconds later, it has 6 holes, but their position has completely changed, 3 upper side, 3 right side. (00:55:25)
Continuity mistake: When smashing the truck in the hangar, the T-850 hits it and it falls down so that the bumper is on the floor. When it shows the T-850 from John's POV, the truck is back up on its wheels, although the wheels are still damaged. (01:29:05)
Continuity mistake: When the T-X steals the car in the beginning, she's weaving in and out of traffic and from her view we see that she is coming up to a truck in the right lane. The view changes to view from outside the car and she's turning into the right lane and driving straight ahead. The truck is gone. (00:07:50)
Visible crew/equipment: Just before John Connor crashes into the car in front with the Tundra, there are a couple of shots shown from inside. During these shots, there is a cameraman visible on the extreme left hand side of the frame, hiding behind a black jaguar. (00:30:05)
Visible crew/equipment: When the TX's crane drags the terminator through the building's glass facade you can see the camera mounted in a cage on the back of the crane when the viewpoint changes to the inside of the building. (00:34:10)
Continuity mistake: When the TX pulls up to Jim's Burgers, notice the umbrellas in front of the store and the "in-out" arrows on the road. Asking for Jose Barrera at the drive-through speaker, she drives in and shoots him from the passenger side of the car and exits on the same side of the building she came in. You can see the front of the store with umbrellas upon entry and exit, yet the speaker has disappeared. (00:16:30)
Continuity mistake: The hubcaps on the hearse come off but are back on in later scenes. (00:59:20 - 01:00:30)
Revealing mistake: During the opening credits, the Terminatrix steals a woman's car. She uses her mobile phone to dial a number and successfully connect to a computer. However, you can see that the phone has no reception, making a phone call impossible. Battery life is the right hand gauge, and signal strength is the left hand one, with no bars. (00:07:25)
Continuity mistake: During the chase scene with Kate's truck and the T-X in the crane, the driver's door disappears and reappears several times.
Continuity mistake: After Kate throws John in the dog cage, moments later she returns to say, Mike Kripke's Basement. The first two cutaways to John there are no bars in front of him. On the third cutaway, there are bars. (00:21:05)
Continuity mistake: During the chase scene when the T-X is driving the crane, the legs of the crane are out in some shots and retracted in other shots.
Continuity mistake: When John talks to Catherine while sitting at the table in a moving RV, watch the explosives he is working on. Position of the charges changes with every shot facing Catherine. At one point they completely disappear from the table leaving only the Glock 18 handgun, and just a second later the table shown full of explosives again. (01:09:55)
Continuity mistake: In the scene when the TX, disguised as Kate's fiance, is in a car with the two policemen on their way to find Kate, the TX kills the police officer who is driving by sticking its hand through his chest. His partner sitting in the passenger seat immediately reaches for his gun, causing his seatbelt to slide off his right shoulder. Cut to a shot from behind him and the seatbelt is back on the same shoulder. (00:52:55)
Continuity mistake: At first, the color of the steering wheel of the police car (the one taking the TX disguised as Kate's fiance) is grey. In a close-up shot of the police officer looking at the TX's arm sticking through his chest, the wheel is now light brown. (00:52:50)
Answer: He was originally in talks - and by some reports, did appear on set for some period of time. While factual answers are in short supply (for obvious reasons), there appears to be a connection to his drug-use habits. For instance, he was checked into a hospital (LA Cedars Sinai) for what friends feared was a drug overdose in April 2001, and has been in and out of rehab over the years. Chances are the production company was unable or unwilling to get completion insurance.
Rooster of Doom