I confess a degree of ignorance. I have only been exposed to derivatives tangentially. Coming from a process control background, I'm familiar with something called a PID (proportional/integral/derivative) controller. Proportional control will only control within a band. Adding integral action will allow a controller to maintain set point. Derivative action is rarely used in highly specialized control situations where anticipatory control is required. Unskilled use of the derivative function will quickly send a loop out of control and usually requires system shutdown and restart. If my analogy is appropriate, there seems to be a lot of unskilled use of the derivative function in our financial system. I also doubt it's neccessity in financial control. The very few who actually use it correctly can either make money or avoid some losses. For the rest, they would be better off going to the crap table.