This guy doesn't always explain everything clearly, but I've come to the conclusion that he basically knows what he's talking about when it comes to the physiology and biochemistry of sexual function in men. At least to the point to where I haven't found anyone with more sensible and credible explanations, especially once you know a little physiology so that you can completely understand what he's talking about. He sells products, but you can ignore that. This is one of the pages he has on vasectomy. The verdict isn't good. If you do a search, you may be able to find others:
http://www.herballove.com/article.asp?art=571
http://www.herballove.com/article.asp?art=571