The particle system in iClone is amazing in terms of its customizeablility, but the particles do not have any kind of collision avoidance... so the particles pass thru any object they encounter....

I would love to be able to create invisible primitive objects (like a sphere or a cube) which would not appear in a render but would force nearby particles to either be deflected or attracted.

Even just simple deflection would be great.  That would enable us to create particle effects ... like water spilling down a set of stairs.... or a cooking fire rebounding around an iron cauldron's base.... or smoke moving through a doorway into a room...