I find this a very interesting conversation. It's certainly given me a lot to consider.
My own method has been to praise when I can. I've very rarely given out 2 x 4's because I'm always concerned that the person is not in position to hear me.
In fact, one time I did hand out a 2 x 4 and the person threatened to up and quit the bb. Not what I wanted at all. So, I came to the conclusion that I'm not skilled at handing out 2 x 4's.
I only want to help people not hurt them.
And I've come to the conclusion that for me...the best method is to praise when they do something right and stay quiet otherwise.