I have to admit that the wingstick is my favorite quick-use item in Rage so far, the main reason being it has saved me from a savage beating many times while reloading my main weapon.
While I usually use wingsticks in situations much too tense to make any astute observations, I've noticed that their effectiveness seems to vary. At times, they will simply lodge into their intended target, killing it, but at other times they ricochet around the room, damaging multiple foes, potentially (I don't think I've actually managed to pull this off). I'm pretty sure I even managed to catch one that I threw in a very boomerang like fashion.
While I haven't been able to figure it out by myself yet, the varying effects seem linked to a multitude of factors, such as the first thing the wingstick hits (enemy/wall), the throwing angle, the type of enemy and so on.
If anyone could shed some light on this, I would be grateful.