I've seen a few of my friends using this site to track their miles and went over to have a gander at it.
I signed up for it because sometimes I forget how miles I ran in a week or I forget to write it on my calendar and then skip a day thinking I ran enough the day before.
What I love about this site is you can route your runs and it gives you an exact mileage you've ran. I love it.
Do you dailymile.com? What do I need to know?