This is a pretty fascinating post I read on Mark Russinovich's blog about SID duplication. Check it out if you haven't already.

http://blogs.technet.com/markrussinovich/archive/2009/11/03/3291024.aspx


At first I was like “whatever he’s lying because I know I’ve seen issues first-hand when a computer is imaged without Sysprep and there are all sorts of issues." However, as Mark notes, one shouldn’t confused the machine SID with the computer Domain SID… so it makes sense in the end.