Maybe I'm unimaginative, but why would I use this? I'd like to see an example or three of why this app is cool. The only thing I can think of is if you're going to go meet someone, but this idea isn't fleshed out on the site.
Off the top of my head: event planning. You often dispatch organizers to pick up props/food/whatever and with Moby, you don't have to call and ask where they are.