We try to convince our puppy people to wait til their puppy is a year old or so before S/N. But primarily because we like to see the growth plates closed. I agree 100% with what Laura said about that on the other forum. However, many times we lose to the pressure vets put on people to S/N before the first season.
All this assumes that our puppy people are responsible owners and will keep a VERY close eye on their dogs.
A few years back there was even a move on to S/N very early, like on the order of 3 months old. I believe that was partially a breeder reaction to people buying a puppy and then breeding it in violation of their contract; just couldn't register it with CKCSC or AKC. Have not heard much about that lately, so hopefully that idea has pretty much died.