Factual error: Will Sawyer puts his wife and son in an elevator - he is going to cut the cable that would put them in a free fall traveling through the floors that are on fire. He instructs her to pull or activate the brake (or magnets in this hi-tech elevator) allowing them to escape the burning building. Given that they are above the 90th floor the acceleration of the free falling elevator would create a force so great that it would essentially push them to the ceiling, which would put this lever completely out of reach.
Suggested correction: They would float.
Factual error: It is absolutely impossible that the fire suppression system would still be operational at the end of the film. The fire would have destroyed all those systems ages ago, and even if the extinguishers / sprinklers themselves are resistant to fire, I doubt very much the cables that hook them up to the building's computer system survived intact.