Are you a runner or walker? How much is that extra body weight slowing you down? According to a recent article in Runner's World magazine every extra pound of body weight is equivalent to 2 - 3 extra seconds per mile!

Therefore if you are carrying ten extra pounds while running the Army 10 miler it will slow you down 3 minutes and 20 seconds (10 pounds X 3 seconds X  10 miles = 300 seconds).
This article specifically is referring to running but it would be safe to assume that a similar rough estimate can be used during both cycling and inline skating too.
 

Trying to manage your weight??
According to a recent study by the USDA, you'll lose 18.8 pounds in one year by upping your daily fiber intake from 12g to 36g.
-Men’s Fitness magazine, May 2007, p 33.