GPS MegaTape makes it possible to measure a distance. It has two modes: a straight tape measure, and, an odometer (tripmeter). In the odometer mode you can record a path you walked or drove. You can also email to yourself or friends. That's a rather nice feature. Do as follows: When you've reached the destination, press the envelope-button on the bottom left and mail to yourself. Then watch your inbox and open the mail you just sent and choose to open the attached file with Google Earth to see the path you traversed.
Of course you can open the attached file with Google Earth on your PC too. While at the PC you might want to save the attachment to your harddisk and give it some good name for later reference. 
Here's a walk I recorded the other day (screen shot from my iPhone). The path I walked is marked with white.