I'm probably off the bandwagon here, but I thought just to add my 2c any way.
I recently read the book by Prof KGM De Cramer (Breeding is a bitch). New technology and methods, makes 'early spaying/neutering something to look into, and apparently on the increase.
I quote: "Some breeder may still have questions regarding early sterilization. There is no increase risk of infectious disease provided the puppies are vaccinated on schedule and are not exposed to a virulent virus at the time of sterilization. It is advisable to postpone sterilisation until 1 wee after the completion of the vaccination regimen if non-exposure to an infectious virus cannot be guaranteed.
Many breeders and veterinary surgeons may still believe that early sterilization of puppies affect their growth, but several research studies have refuted this. Obesity can occur in both neutered and intact animals as it is influence by factors such as diet, calorie intake and activity levels. Obesity is more likely in spayed bitches and neutered males, irrespective of whether the surgery was permed at an early age or not.
Dogs neutered at traditional ages can develop urinary incontinence within days of the surgery or several years later. Oestrogen-responsive urinary incontinence can occur in up to 4% of bitches which are spayed at the conventional age. To date, there is no evidence that suggest that the incidence of urinary sphincter incompetence which leads to urinary incontinence is higher in bitches which were spayed at an earlier age.
In conclusion: there is no conclusive evidence that the early sterilization of young bitches holds any increased risk other then the normal risk associated with sterilization at a conventional age. A Bitch should be sterlise as soon as possible or as soon as it's decided, not to breed with her anymore.