Although they do still work long hours, there is a now a law prohibiting residents from being worked over 80 hours per week. It's called the "Libby Zion Law." The law is in place because of a famous malpractice lawsuit due to a resident physician that administered pethidine when the patient was already on phenelzine, causing her to die. This caused a fatal drug interaction that the resident should have understood was deadly.

It's applied by the individual programs, but residents often have multiple sets of obligations :(