Ungrounded systems are actually fairly rare in the US. You won't see them in residential at all. It is usually a critical industry where they can't handle a shut down due to a fault. They are required to have fault detectors so they know they are one more fault from a shut down.
Some lab situations may have an ungrounded supply and IBM did not ground the secondary of their "convenience transformers" that gave the techs 120v for their test equipment. It was really our little secret tho because the NEC/OSHA/Inspectors would not approve. Most of the techs didn't know it either.
