Visible crew/equipment: When the subway train with Annie and Will departs (the train goes to the right side of the screen), there's a close-up of the train. Then, in the lower right corner (during two seconds) you can see a camera, a cameraman and two crew members next to it, reflected on the windows and the shiny surface.
Factual error: Throughout the movie, we see various shots of the Ripley computer system with some sort of fog being pumped around the circuit boards inside. Presuming that this might even be a coolant of some sort, the way in which its being directed and not dispersed would create moisture on the electronics and easily short circuit things.
Plot hole: When Will is on the airplane talking to his mom, there's a knock at her front door and she says, "There are men in suits here". However, when we see her open the front door, it's covered in thick frosted glass which would make it impossible for her to determine what the people were wearing.