Pit bulls were originally bred as pit fighting dogs. For this they have a few innate traits. Any innately bred dog trait CAN be trained out of them by their pet parents. PLEASE be responsible with your dog!
1) They had to be tenacious and NEVER give up in a fight unless their owner called them off.
2) They had to ALWAYS follow their commands, especially in the case of being called off
3) They had to be very dog aggressive.
4) They had to be safe for the spectators to be around.
As pit bulls were bred solely for their "fit" for these 4 things, rather than their looks, they have much less inbreeding than other breeds of dogs.
When you get a new pit bull puppy, it is important to socialize him with other dogs of all types in order to train out his dog aggressiveness.
Pit bulls are generally very friendly dogs, but, unsocialized, can and WILL treat any outside dog as a threat to his "pack" and it will not be pretty.
DO NOT EVER provoke a pit bull. While they are not naturally aggressive dogs, they WILL NOT give up if they do end up fighting. If their owner hasn't strictly trained them to heel on command, the only way to end that fight is for one or the other to die. NO ONE should want that.
When adopting a pit bull make certain that you are going through a reputable breeder. Some breeders do not care about demeanor, or specifically cater to the "thug" crowd that want a pit bull for their bad reputation. Make sure you aren't getting a god that was bred to be aggressive.