We manage all our site security via AD group memberships. We are currently in the process of folding four AD domains into a fifth domain that already exists. Our farm is in one of those four domains but it will not be moving due - we'll handle that when we migrate to SP2013.
Given those considerations, does Move-SPUser essentially function as a user merge tool in that scenario? We have some users with two or even three logins to the site, and my hope is that we can use Move-SPUser to merge them all in order to preserve author/editor metadata on SP objects.
Assume we are moving domains B and C to A. User Bob has potentially created content on B\Bob and C\Bob. We can use Move-SPUser to migrate B\Bob to A\Bob. What happens if we then migrate C\Bob to A\Bob? Does all the existing content associated with A\Bob get "Unknown User"? Or do the IDs all get overwritten?