If you’re not working for a data center fabric vendor (in which case please read the other today’s post), you’ll probably enjoy the excellent analogy Ethan Banks made after reading my TRILL-over-WAN post:
Think of a network topology like a road map. There's boulevards, major junction points, highways, dead ends, etc. Now imagine what that map looks like after it's been nuked from orbit: flat. Sure, we blew up the world, but you can go in a straight line anywhere you want.
... and don’t forget to be nice to the people asking for inter-DC VM mobility ;)