i put a scotts damper on my fe400 awhile ago and told myself after spending the money that it was worth the investment. now, granted, i'm old, fat, and slow (getting slower all the time), but when i put it on my fe400e, and would switch back and forth riding the 400e with and 400 without, i can't say i miss it. there are times when it is an advantage, but those times are when berserking thru washes full of rocks, and i try to avoid those nowadays. i ride the same rocky, twisty trails on both bikes and can go faster on the 400 because its lighter and reacts better. it seems the damping settings i use tend to be heavier than what i probably need, but i use them so i'll know the damper is working, and that causes the steering to be less responsive than the nondamped bike. at this point, i'd agree with those that say if your suspension is right, and you don't do baja, you don't need one.
ned