I found several references (see below) on blogs that the setspn.exe utility should be run from either a client or server machine in the domain, but not from the domain controller itself.
http://www.petri.co.il/how-to-use-setspn-to-set-active-directory-service-principal-names-2.htm http://blogs.msdn.com/b/russmax/archive/2009/10/20/configuring-kerberos-authentication-in-sharepoint-2010-part-1.aspx
What is the reason for this? What happens if I run setspn.exe on the domain controller anyway? I'm asking because an SPN I set disappears after a little while.