Possible Story: Protective Capacity http://www.focusedperformance.com/articles/effort.html
Possible Story: GoldCards (Variation on XP from Connextra)
"Iterations, velocity, "done done", and slack all conspire to accurately estimate how long your work is going to take. They don't prevent schedule overruns, but they warn you about them in time for you to do something constructive." --James Shore and chromatic, The Art of Agile Development (forthcoming)