Depends on who you talk to LOL.

It's a fiery debate. Some fans say that Staffies and Pitties were the same breed up until one branch started breeding exclusively for show while the other branch bred, well, not for show. Others say that they're one and the same.

If I remember correctly, AKC registered AmStaffs can be dual registered in the UKC as American Pit Bull Terriers, whereas UKC registered Pitties cannot be registered as Am Staffs in the AKC.

You also have to make a distinction between Am Staffies and regular ol' English Staffies.

Here's BADRAP's take on it:
(Scroll down to "AmStaff or APBT"?)
http://www.badrap.org/rescue/breed.cfm