I have heard of this before, and it was presented by people who were very much for it.
My first reaction is that it is totally wierd.
My second reaction is that in developed countries, men who want to do this are doing it for themselves, not the baby. Men are perfectly capable of close, nurturing contact with their babies without having to suckle them. In developing countries, where additional nourishment is actually an issue, I have a hard time seeing those (generally) traditionally minded dads engaging in the womanly art of breastfeeding.
My third reaction is that if I saw my husband trying to breastfeed our baby, regardless of his motivation, it might well be the end of our sex life!
Overall, I think it's unecessary, and I'm convinced that men who want to do it are doing it more to nurture themselves than their children.