I remember seeing this in another game.. You have a regular attack that you could use normally, than an attack called Aimed shot, that you could used each time, but not while doing other things.
I used it nearly every encounter when I played the ranger, which was about 6 hours worth of 4e gaming with the ranger (the other five hours with other classes).
Fox's Cunning was really useful, and is great when combined with a Fey Step (spent as an action point).