It seems the general consensus here is that "3D" involves hovering. There are a significant lot more maneuvers that just that. Tumbles, Waterfalls, Blenders, Parachutes, Walls, Falling Leaf, harriers, Rolling maneuvers and many others are generally all considered 3D.

Would the club that mandates "circuits" accept a rolling circuit? Would they also accept (or not accept) IMAC routines?

The thing is that the pilot who spends most of his flight hovering his plane is generally annoying to most, especially as many of those tend to feel a need to constantly blip the throttle (usually because their choice of engine suffers from a poor mid range power curve).

As has been mentioned by so many, it is al about respect. True "3D" routines are no more and no less problematic to other flyers than any other aerobatic routine. In fact a flyer down low is less of a problem to other flyers as long as he stays down low and dosn't come near to other pilots. It is when he pulls up that the problems occur, same as a pilot practicing an IMAC routine will do f time to time or a Warbird pilot will do after a successful low pass down the runway.

Now I am going out to practise my rolling loops and knife edge spins - 3 mistakes high and along the aerobatic line.
(Is there such a thing as a rolling spin? - maybe around the pitch axis )