I carry the GlobalSat DG-100 with me nearly all the time in order to geotag the hundreds of photos I take each week while bicycling.

I uploaded a GPX file from the GPS logger into uTrack and it outputted a nice report that gave me my average speed. It seems to know a good way to calculate average speed that ignores waypoints recorded when I'm stopped. If you use a spreadsheet application and its AVG() function to calculate the average speed based on the speed output of GPS Visualizer, you will get an incredibly low number. For the report below, it told me 1.86 MPH.

Download uTrack-created report of two tracks.