I have a Drill Doctor, and it works pretty well, but I generally just freehand grind, it's way faster. Besides taking a fair amount of time to set up, Drill Doctors only handle relatively smallish bits which are more economically just replaced.
Lisle makes, or made a really nice sharpener, and I'd let one follow me home for the right price. mrpete222 did a series on refurbishing one of these a while back