See Agents Everywhere

Pitfalls of Agent Development

You need to choose the right grain size
What are the agents in your system? Think carefully about this.
Try out different agent instantiations to see what emerges.
If you have too many agents you might end up with undesired emergent behaviors. Be careful. Keep interactions to a minimum. Keep protocols simple.
If you have too few agents you will end up placing all the functionality on a few.