I used to be a huge advocate for early/spaying neutering until I did alot more research. It defintly does have it's ups -- less recovery time being the biggest. Also, I don't think the vast majority of people know how to train out behaviours that are a result of hormones. Better to nip the hormones in the bud so the dog can have less training difficulties, than to end up in a shelter later in life because of issues resulting from hormones.
I've never had issues with hormone related behaviours, but my dogs are also properly trained. Average Joe-Blow may have no idea how to train a dog.
I think it's great that some shelters alter so early. I know many SPCA dogs that were sold on a contract, only the owners ignored it and bred the dog anyways. I have my own ways of doing things (waiting until the dog is full-grown), but if someone wants to spay/neuter early I certainly won't have any qualms about it. The earlier it's done, the less chance of the dog breeding. Those of us with intact dogs always have to keep in mind that our dogs are always at risk of being bred, whether intentional or not. We have added responsiblity that some people can't or don't want to deal with.
As long as it's done at some point, and the dog is kept safe from breeding if it's done later, than to each his own, I say!