I had a little bit of time this morning to try out some more stuff with the navigation meshes in Unity and was really blown away at how easy it is to work with them. As you can see in this screen shot I just took my little zombie cubes and player object and placed them on a Unity terrain that I sculpted really quickly. I baked a navigation mesh for the terrain with a click of a button and boom! As with most tasks in Unity...it just works.