For anyone who is interested in Formation Movement (units moving in formation along the path) I've created a set of scripts to do exactly that. I thought it would be a nice idea to give something back to the A*Pathfinding and Unity communities so these script are now available as open source under the MIT license.
If you're interested take a look at this Github repository.
This solution requires the units in the formation to have a rigid body or character controller component and includes support for coupling animation to movement and sound on the units (like marching boots). Although the solution now also works with Unity's navmesh the best results on terrain can be achieved using A*Pathfining.
Two more quick impressions: instruction video and results on terrain.
Hope you like it and find it useful.