What's one of the biggest problems for runners and walkers, particularly those who are just starting out?
Knowing how far you've gone!
Somebody pointed MJ to this great website: http://www.usatf.org/routes/map/. It uses Google maps to let you map out a route, and then tells you how long that route is. It even puts mile markers up for you.
You just zoom in to your neighborhood, click your starting point, and then keep clicking along your route to extend the route. Every click creates an as-the-crow-flies line from your last point, so don't go running through any backyards.
It also has a "there and back" feature, if you just have a turnaround point.
I spent so much time playing with it today, I ran out of time for running.