Let me start by saying that my computer is currently not available so I do not have access to the dozens of links to back up everything that I am about to post. As my internet connection on this computer is tentative at best, I do not have the HOURS it would take to find those links AND post. So you will either have to take some of what I am about to say on faith. You could do the research yourself or just think I am a liar - it really is up to you.
First off - according to the American Kennel Club and the Canadian Kennel Club, there is no such thing as a Pit Bull. You will find that in almost every single breed ban there are three breeds listed ("and mixes thereof") - the American Staffordshire Terrier, The Staffordshire Bull Terrier and the Bull Terrier. While there are other registering entities in North America, these two are the most "reputable" and in most circles considered the authorities. So we will base the following facts on this assumption.
Now - since I am a U.S citizen, I spend more time on the AKC website so I will be using the information gathered there in the last 10 minutes to make my point.
In 2006, AKC registered a total of 4,312 puppies of the breeds mentioned above. If you just use this number to figure out the percentage of "pit bulls" that bite - you will see that the number is 2.06%. That is a remarkably low number and doesn't begin to take into account the number of dogs registered in previous years, dogs registered to other registries, dogs that are not registered or "mixes thereof".
When you look at this - you will see that banning breeds is ridiculous and so is placing severe restrictions on "viscious breeds" such as the ones you mention in a previous post.
Here is a rather novel idea - uphold the laws that were on the books before the breed ban!
Every single city that I have ever lived in has had laws on the books pertaining to vetting, leashing, and registering dogs. I think you will find that, almost without exception, dogs that attack and kill people are intact, loose, unregistered dogs.