I found myself looking for this query for the second time now and finally decided to post it on my blog [8-|]
This query enables you to find out if your connections towards your SQL server are using Kerberos instead of NTLM. This may help in your troubleshooting or confirmation for your Kerberos implementation on SharePoint.
If found it back this time on the blog of Marc Valk (http://www.marcvalk.net/2009/04/sql-query-to-identify-kerberos-or-ntlm-connection/)
FROM sys.dm_exec_sessions s
JOIN sys.dm_exec_connections c
ON s.session_id = c.session_id