Here is an interesting 'sql security' discussion I had during the SASSUG usergroup interaction with regard to BUILTIN\Administrator role from SQL Server 2008 onwards. Since SQL Server 2005 the instance has been classified as 'secured by design...
SQLServer-QA.net - Knowledge Sharing Network (SSQA.net)
Tue, Jun 29 2010
Filed under: Filed under: sql server, security, dba, access, best practices, dac, registry, windows authentication, control, dedicated admin console, builtin\administrator, uac