Revealing mistake: When the Empire State antenna falls down the wires holding it are visible.
Revealing mistake: In the New York battle scene, after Ursa distracts Superman, Non punches him and he goes flying backward into a building. Watch very carefully along the bottom of the screen. You can tell that Superman isn't even matted in from the chest down. Where is the rest of him?
Revealing mistake: When Non tries to fly at the end of the film, but falls into the bottom of the Fortress of Solitude, watch closely. He appears to hit some sort of safety pad after he falls, making the fog around him disperse very briefly, which shows him safely land on the pad. The fog quickly comes back and covers him as he ducks his head down.
Revealing mistake: When Non goes through the pavement, the hole reveals it's a foam made floor.
Revealing mistake: During the big fight in Metropolis, the close-up of the pram shows its empty. It must a very expensive pram for the mother to protect it in such a heroic way.
Revealing mistake: When there are multiple Superman's in his home, Lois Lane runs to one of the fakes. It seems as if she is the fake because her image becomes slightly transparent as she runs through him.
Revealing mistake: Near the end of the film when the 3 villains enter the fortress, Ursa throws Lex Luther off her back and flies away. You can clearly see that it was a stuntman and not Gene Hackman.
Revealing mistake: When Zod lifts the man from the motel, you can see the power pole through him, showing the composite of the time.
Revealing mistake: When Lois jumps in the river, she is replaced by a very obvious mannequin that floats stiff. Furthermore, the current tilts the dummy and its two arms bent like a sex doll's are perfectly visible.
Revealing mistake: When Superman arrives at the tropical place, the sea doesn't move, revealing it's a very obvious still picture where a flying Superman has been inserted.
Revealing mistake: After the army jeep drives through a House in East Houston, notice the driver's stiffness despite the crash and fall, revealing it's a dummy.
Revealing mistake: When the 3 villains start blowing at the people in Metropolis, the papers come blowing from the left and right sides of the set, revealing where the huge fans where placed to achieve the effect.
Revealing mistake: When Ursa throws the sewer lid at Superman a sticky object protrudes from his back, revealing the mechanism that pulled him backwards.
Revealing mistake: Right when the Metropolis fight is about to start, Superman flies to the Daily Planet and passes by a building. Check the pattern on the windows and you'll notice that the same small door on the left appears almost everywhere, revealing that a miniature was used.
Revealing mistake: The villains send cars flying through the air. This was achieved with detailed scale model cars in a scale model Metropolis. But in order to mimic the blown-away citizens they use cheap mannequins that move on some sort of conveyor belt. (01:43:50)
Revealing mistake: When the villains blow away the stuff in Metropolis, the fire hydrant falls down and reveals it wasn't fixed to the ground, a blatant prop.
Revealing mistake: When Non punches Superman and he crashes against a metal wall, there's a brief shot where Chris Reeve's stunt double is very noticeable.
Revealing mistake: At the Fortress, when the villains and Superman play the appearing/disappearing trick, there's a shot with 4 Supermen onscreen, a special effect which was achieved with stand-ins. The one in front of Zod, and especially the one next to Lois look nothing like Christopher Reeve.
Revealing mistake: When Luthor is about to climb up the balloon his bald cap wrinkles by his nape.
Revealing mistake: In the prison laundry, Luthor's bald cap is very noticeable, especially by his sideburns.
Answer: Superman was be able to kiss Lois in such a way that the heightened emotion wiped out her memory of his identity. To answer your second question, even though Lois promised not to tell anyone, Superman decided he does not want even her to know his secret identity.
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