Shroom -- there is a fuction on many modern 35mm cameras that allows you to alter frame rate within a shot; that is, speeding up and/or slowing down, in combination with narrowing or widening the iris so that the light exposure stays constant. That's probably what was done with DD, since it's a cheaper way to do it than optically slowing down or speeding up the film within a shot in post(which is also possible to do, and was done before this gizmo). However, it doesn't make choreographing any more difficult. They just stage it regularly, at normal speed, and then Kelly and his DP decide at which points to slow it down. The camera does the rest.
Some of my favorite examples of long, beautifully choreographed takes with a lot of camera movement are: I Am Cuba
, which was one of the earliest films to make the camera completely omniscient and defiant of all laws of gravity, the opening shot of Boogie Nights
, which lasts a good 5 minutes and introduces every major character as well as the film's milieu, the final shot of Much Ado About Nothing
(which is so fantastic and complex that most people never notice it's all one 10-minute shot; it's just too impossible to believe), and of course the entrance to the club in Goodfellas.