I also use this site for planning out my shorter 5-6 mile runs during the week. What's really cool about the site is that you can create a personal account, design a running route and then save the route if you really like it. Then you can share that route with other runners.
For example: Here's a little 6 mile loop through the hills of Caughlin Ranch that JBird and I will be running this afternoon.
Check out MapMyRun, and we can all start sharing our favorite routes.
Dennis