Don't take this as gospel, but I seem to recall reading an article by an elite powerlifter (I think Ed Coan) saying that the deadlift is best once trained every 2 weeks.
Ed, or whoever wrote that article, was saying that when you train the deadlift, you actually do more harm than good in the short-term. It is so taxing to the body, you can easily overtrain by doing it too often. (This only applies if you're truly working hard on it, and using maximal weights)
He would do it every 10-14 days, just to practice the lift, and get his body used to the movement. He felt that the best way to improve the deadift was to train accessory muscles, and build them up..... hamstrings, quads, abs, lower back, grip strength, traps, lats, etc.