How far was that run?

In my brain I have been thinking that there has to be a Google Maps mashup that you can use to calculate the distance you have run. Something that might be called a Google Pedometer, perhaps?

Lo and behold, it does exist! This is an excellent tool for estimating how the distance of that run you just went on. (Note: once you've found your starting point, click on the "Start Recording" button and then double-click on the map to set waypoints)

In looking for such a tool, I found a blog that lists various Google Mashups. So if you're looking for some other useful mashup, maybe you can find it there.