For those doubting Thomas’ who question Active Directory’s near infinite scalability there’s a white paper you can read on this topic. Ever wondered what the maximum number of objects that could be stored in AD? Read the white paper to find out that the answer is 2.15 billion objects (that’s 2**31 minus 255 by the way). Or that the maximum number of SIDs is 2**30 or about 1 billion. There’s a lot of good information in this paper related to maximum number of group memberships for security principles, maximum number of group policy objects applied, etc. You get what I mean.
So if you need this type of data or run into someone who still is doubtful of Active Directory’s incredible powers point them to this white paper.