Those of you going on about how barabric it is and comparing to female circumsion, it sounds like you haven't a clue. The latter truly is barbaric, inflicting great pain and agony whilst presenting no benefits, with the former, you get it over and done with, it hurts for a few days and then is gone. Never given me any touble in 22 years.
Of course, if you do it in adulthood, hurts like blazes. That's why Judaism says eight days. I'm not really sure why Muslims do it in later childhood, but it's still better than having it done as an adult.