Blender keyed particles system with path option - Tutorial

The two particles systems to be keyed must be created first.
In this example, one for the cube and one another for the sphere.

Then create a third particles system that will key the two first PS.

As you can see, the particles goes from one object to the other.

Now activate the path option, this will display the path for each particles between system1 and system2.

Play with path options (start / end) or particles system option like initial velocity...

You can view some demos videos here:
intro - simple keyed particles - http://youtu.be/8iXK6OuX2V0
intro - keyed particles with path option shaping a spider web - http://youtu.be/F6IMLSWLw5E

Let me know your comments.