Hey there- hopefully I can help you out with some of your concerns. I've been in Shibas for about 10 years, and currently own one neutered pet-quality dog, and one intact show quality bitch.
As a general rule, I'm not too quick to reccommend Shibas as a first time dog for anyone. That being said, my first dog was a Shiba, LOL. I studied several breeds over a time period of a few years, and by the end, was convinced a Shiba was for me. I talked to several breeders, got a feel for temperaments, and made the plunge. They are by no means an *easy* dog, but if you're willing to devote the time, you can make it work. I did, and the result is two wonderful companions I couldn't imagine being without.
Now, on to your concerns:
Shibas, as a general rule, are a dog-aggressive breed. While I've met a few that get along famously with every other dog they meet, most do not, and you shouldn't expect them to. Mine *tolerate* other dogs (they know what kind of behavior is expected of them), but they will never be the type to play happily for hours on end with other people's animals. In short, if your looking for a dog that you can enjoy taking to the dog park, think again about Shibas.
In terms of human aggression- without a doubt, steer clear of ANY breeder who tells you that this is a human-aggressive breed. That is a load of BS, and such behavior shouldn't be tolerated for a second. Shibas bond very closely to their family, and could pretty much give a flying rip about anyone outside of it, but you should never see a Shiba display outright aggression towards a human (unless given due cause). Their attitude is a sort of "does God swat flies?" mentality.
Iffy temperaments *have* been an issue in this breed in the past, but as a whole, I believe they are improving. Choosing a great breeder is your greatest insurance for success in this department. If you've found a couple breeders you're interested in, you are most welcome to PM me, and I might be able to help you out.
When it comes to Shibas and newborns/young children:
My mom had a baby around the same time that we got our first Shiba, and we had absolutely no problems. My little brother and Tai get along famously. People often ask "are Shibas good with kids?" My reply is an ecstatic "YES! IF the kids are good with Shibas." Both children and pets can be taught respect for one another. Most people wouldn't tolerate getting poked in the eye, slapped, etc. yet we expect our dogs to be angels in the exact same situations. The key is to remember that dogs are *animals* not little people in furry coats. They do not operate under our social mores, and expecting them to does both you AND your dog a disservice. Never leave the child unsupervised with a dog (this goes for ANY breed- even Goldens and Labs), and you should be fine. We've yet to have an incident in our family. As a whole, Shibas don't make great "kids dogs," because they tend to be more aloof, but they make wonderful "family dogs."
Obedience classes are a must, if you want a dog you can live with. That being said- shop carefully for your obedience class. Most Shibas don't take kindly to "traditional" corrective forms of obedience training. In other words, throw the The Koehler method of dog training out the window. If you teach primarily with corrections, your Shiba will shut down and lose all respect for you. They do *far* better with positive reinforcement (operant conditioning) techniques. Feel free to visit the training forum and look for posts by Doberluv and IliamnasQuest, who both do an excellent job of explaining why positive reinforcement is a good choice for Shibas.
I hear a LOT of people say that Shibas are "stupid" or "hard to train." Nothing could be further from the truth. This is an extremely intelligent (bordering on cunning) breed. You will not be able to train a Shiba like you would a Golden. Understanding the breed's history will help you realize why this is true. This ancient breed has been cultivated for centuries to track and hunt wild boar and bear in Japan, while the Matagi (hunter), followed at a distance. Therefore, it was never in the dog's best interest to wait for instructions from a human not in the thick of the battle. Hesitation while listening for directions = a good way to get gored or killed. That being said, your Shiba will want a *very* good reason as to why it should follow *your* directions!
It all comes back down to positive and *fun* training techniques. (Shibas LOVE agility). One other thing to keep in mind- this independent streak makes the majority of Shibas TERRIBLE off-lead dogs. If you want a reliable off-lead dog, drop the Shiba from your list immediately. I've met two in my life that I found were decent at best.
Exercise is a definite must for these guys- they are NOT lap dogs. Any athletic pursuit you are interested in- they will be too. (Unless it's swimming, in which case they will happily stare at you from the sidelines, wondering what on Earth would possess someone to go into cold water VOLUNTARILY).
Grooming is pretty low-key with Shibas. If it wasn't for the fact that I show my dogs, I could easily get away with bathing them 4 times a year. They're incredibly fastidious, hate to be dirty, and never have that "doggy smell" that people complain about. They DO blow coat twice a year though- and then the house will be FILLED with fluffy puffs of hair. The vacuum will become your best friend at this time, LOL. A bath and comb out will shorten this process though.
Please excuse the length of this post- as you can probably tell by now, I am absolutely in LOVE with this breed! Don't hesitate to ask more questions- I'm only too happy to help a prospective new Shiba slave...err...."owner."