Do you use a mane and tail shampoo on your horse? how often?

I've never really used shampoo. When I need to get my horse clean I've just used water. The lady who has a horse boarded at the same stable was making me feel guilty, giving her horse a "proper" wash the other day.

I've used shampoo and conditioner before shows, but otherwise its normally just a good hosing with some scrubbing to get the dirt out. Since most horses are kept out all day its not smart to strip out the natural oils in their coat. Now if she is one of those prissy horse owners with a dozen different blankets/sheets and keeps the horse mostly inside it doesn't much matter if it makes her feel better.