In my area there is a vet that actually will neuter at age 10 weeks or more, but I wouldn't recommend it. I had a friend get thier pup spayed at 4 months and now at 1 year she leaks urine all the time. Just a few drops frequently(even after she just went outside), but I highly suspect that it's from spaying too early.
Basset your right.....I have a litter of rotts that are going to be altered starting at 12 weeks. Well actually 2 days before they are 12 weeks. I have 3 dogs here that were all altered before 6 months and they are all fine.
When you should alter your dog depends on the age. Males - it is safe to neuter as soon as both testicles are descended, or by six months if you have a monorchid or cryptorchid dog. It is a completely non invasive surgery (meaning, if the testicles are descended the vet never even goes into the abdomen so there is virtually no risk involved). We have had several puppies neutered as early as 4 months with absolutely no problems.
Females - if you have a breed that goes into heat at an early age you need to spay early. The chance of incontience is less than the chance of breast cancer. Your chances of breast cancer in a female dog triple once she has gone through a heat cycle. Incontience is rare. It does happen, but from what I have learned in my research, good vets know what they are doing on an early spay and your dog should come out of it fine.
The myth used to be that every female should have a litter before spaying, and that male dogs should either be a year, or sire a litter. Now vets and the general population seem to think 6 months is the new ideal time frame. Actually, younger is better as they bounce back more quickly.