I generally had good luck with them. Once, while a buddy of mine was fliming, we caught onvideo the arrow striking a weed on it's way to a turkey. It appeared to catch one of the blades and cause the arrow to twist in flight right before it hit the bird. Still hit him, but he got away.

Another guy I know hit an antelope quartering away at a pretty steep angle. The arrow turned on impact, and followed the ribs - coming out near the shoulder. Lots of blood. Finally found him. Bled out from artery cut in shoulder. But the arrow never did actually penetrate the ribs.