One studded tire in front is sufficient to maintain control and keep from falling. Who cares whether you fishtail? As long as you are upright and moving you are fine. Because most of my bike's weight is on the rear wheels, front studs alone produce no discernable added drag.
However, there is more to riding than just staying upright. You may have problems on hills without rear studs. Starting out up even a slight grade from a stop can be difficult. When descending a hill, overuse of the front brake can drop you, and rear braking action is limited by the lack of studs. Furthermore, if things are really slick, you may have trouble even walking the bike. I would say that the answer depends strongly on how hilly your area is. Personally, I use them on both front and back.
You might consider mounting just the front early in the season when ice is rare and mount the rear later when it is common. I find it less hassle just to put them both on in December and leave them until March.