Troubleshooting Delegation in SQL Server
I just came across a good article by Keith Brown on a common trap when setting up SQL Server with kerberos delegation. As he noted, the port number for the Sql Server Service should be specified when setting the service principal name (SPN).
Delegation is a powerful feature of Active Directory but can be difficult to setup. It can be used to allow SQL Server to impersonate the user when connecting to other services: such as BULK LOAD connecting to a network file server. Or for middle tier applications to impersonate users on other servers. A detailed explanation of delegation can be found here.
Microsoft's whitepaper on troubleshooting kerberos delegation has more detail on setting up SQL Server, including linking servers with delegation.