I've been running as part of my daily workout for a while, but never had any clue what distance I was covering, other than a rough estimate based on how many songs my iPod gets through during the run.
I started looking into getting a pedometer, and then found this site. Drop in a series of waypoints to make up your route and it gives you your total distance. Add in some additional info (time it takes, your age, height, weight, etc.) and you can also get the number of calories burned.
I'll probably still pick up a pedometer for cases like today where I get lost and have no clue what street I'm on, but now I know that my usual post-Bowflex run is actually 3/4 of a mile rather than 1/2.