Marksmanship is expensive at 3 points, and I often see it misused. I've seen many an odd build with Marksmanship and only two have actually worked. The first was with Darth Vader (as he can take two actions) and the other (the one I use) is Ten Numb to go along with his unique skill.
Any other Marksmanship builds out there that fully take advantage of this upgrade?