I've recently been using a pedometer tool for my running and orienteering that breaks down your actual route into a discreet number of segments, and then sums the segments...all imposed on Google Maps - either satellite or map view. In addition, it will estimate calories burned during your run, and allow you to save your course to your own url. All for free.
It is a very easy to use tool, and is available at:<
http://www.gmap-pedometer.com/>
For an example of a recent orienteering run of mine (an October 15, 6.1km Green course at Palos North - site of CAOC's 2002 A-meet) go to <
http://www.gmap-pedometer.com/?r=521088>
Perhaps this is old news, since this cool tool has been out for over a year, but I just found out about it. I think it is particularly helpful when going out for a training run on streets...you can get a pretty accurate idea how far you've run.