I have read about quite a few breeders that neuter early. I saw this:
Breed (s): Yorkies
Breeder/Rescue: Cheryl Nims
How many years early spaying or how many litters: over 10 years
Aprox. age of pups when procedure was done: 8-10 weeks
Personal Observations and Experiences:
I am Cheryl Nims and raise Yorkies. I have been early neutering the males for over 10 years now and have never had any bad results. Most pups are 8-10 weeks old and weigh between 1 3/4 and 2 1/2 lbs. Usually by the time I get them home from the vet they are up and playing like nothing ever happened.
I strongly recommend early neutering to my customers but some are hard to sell on it as their vets are so misinformed. I think the time is coming soon that I will not let them make the decision and just neuter all the males. If they do not like it that is just tough. You can't beat a neutered male for a pet.
I am not that experienced with the early spaying of female pups. The last one done experienced complications as she was not physically normal. It was quite a scare but the pup did recover. I have done early spays that were very successful but the complicated one set me back a little.
My vet does the early neutering at a nominal charge as she feels it is a service worth doing to help the pet overpopulation. This can save my customers hundreds of dollars and perhaps the life of their new pet. I would strongly recommend early neutering. All the evidence is in favor of it.
http://regaliapyrs.tripod.com/early_spay_neuter.htm
Also, at the bottom of this linked page, there are a number of links to articles about early spaying and neutering - both for and against.