Check out http://www.gmap-pedometer.com. It's a google maps hack that lets you calculate the distance of your running route. You click "start recording" and simply double click on each point that you want and proceed to the next one on your intended route. The cumulative distance is shown so you know how far you would've run. This is a very useful tool for runners who would rather not have to measure their route in a car or wear a GPS unit.
Just out of curiosity, I compared it to ask.com's maps feature that I wrote about in my last post. For a specific route, I calculated the distance using both these methods. What do I get? Exactly the same distance. I think they differed in the second or third decimal point but that could be attributed to where I placed my points on the maps. This one was slightly faster than ask.com, but it's not exactly a fair comparison since this is a utility that was built on gmaps. It could have as well been built on ask.com. Overall, I think it's very good.