It is my understanding that most US carriers do not train for circling approaches and certainly not when it is below 1000/3??? I have also heard that "No Circling" is a restriction on some type ratings.????
Yes, however, on some FAA certificates, circling is limited to VFR conditions only.
Depends on the individual airline.
We circle regularly, so therefore require pilots that are proficient in this maneuver.
I'ts not that difficult, just needs practise.