I think usually when this topic comes up on the board that people aren't very concerned over the ferrous particles. It is the non- ferrous ones that seem to be important (like in the Hall of Wisdom acid test for flaking rockers).
http://www.ducati.ms/forums/80-hall-wisdom/29950-oil-change-drain-plug-screen-particles.html
http://www.ducati.ms/forums/80-hall-wisdom/29950-oil-change-drain-plug-screen-particles.html