Haven't tried it yet, but this sounds useful:
"Now, with Google Earth 5.2, we’ve added the ability to view elevation, speed, and other data as a graph directly in Google Earth. Just connect your GPS device to upload your track, and select “View Elevation Profile” from the menu. This will bring up elevation and speed graphs. If your GPS device records additional information such as heart rate or cadence, these will also be available to view in the graph. You can also see statistics such as total elevation, maximum slope, and average speed. You can select a portion of your ride and get statistics for just that section."