Continuity mistake: When leaving the Daily Planet for the first time together Clark gets stuck in the revolving door behind Lois. He lets her go through ahead of him and gets in the next section as the door revolves. Cut to the exterior of the Planet when they emerge (just before they meet Rex Reed) and Clark is in the same section of the revolving door as Lois.
Revealing mistake: When Lois is at the heliport, watch the wind flag on the left: when the helicopter arrives, the roaring wind from the vanes makes the flag move up and get stiff. In the close-ups, you keep on hearing the sound but the vanes are off screen. Watch and you'll see the wind flag is down, thus revealing that the engine is off and that the sound we are hearing is fake.Sacha
Other mistake: When Superman and Lois are flying through the clouds, there are a number of shots in which we see Superman from Lois' point of view. If you look closely, you can see that Christopher Reeve is not being suspended in these shots, but is, in fact, kneeling to look as though he is flying. You can tell by the profile of the red trunks.
Continuity mistake: During the Golden Gate Bridge crash sequence, a reversed shot of a life-sized 1972 Trans-Am braking hard is shown. The next shot shows a model car smashing into a model school bus, and the car is suddenly a 1965 Corvette. The fimakers have painted it red & white so it resembles the Trans Am. (Timecode is for Director's Cut) (02:09:10)