I have the 24" HF breaker bar, and the thing flexes so much you swear it's gonna snap - but it never has. It still doesn't inspire much confidence, but it hasn't broken. I also have the HF 3/4" quick-release breaker bar, and it is pretty stout - I have a lot of confidence with it.
I was looking at and playing with the Craftsman 1/2" drive breaker bar at Sears, and it just looks and feels solid. I think I'll try one if they go on sale.