Factual error: When Clark speaks to Jor-El for the first time in the Fortress, Jor-El says "I will have been dead for many thousands of your years..." Fine in theory - Baby Kal-El travelled to Earth at above light speed so time passed differently for him. However, as such, wouldn't Jor-El have seen Earth as it was thousands of years ago? Which also makes there a problem with all the things Kal-El was taught during his voyage to Earth, as Jor-El references Einstein by name, for instance, and he would not have existed at the point when Jor-El sent him to Earth.
Factual error: When Superman is turning back time by flying around the Earth, right before he starts orbiting the Earth is spinning way faster than it actually should be. If the Earth actually spun that fast, a day would pass by every 1.44 minutes.
Answer: Just to clarify: Superman didn't spin the Earth backwards. We just see the world turning backwards when he went back in time. Of course this doesn't answer your question and it shows how difficult it is to write a good time travel story that doesn't leave the audience thinking of better ways to solve problems.
I guess the way they wrote it, Superman got to be the hero and also get the girl, not really too bad of an outcome.
briggs