http://blogs.technet.com/b/rob/archive/2010/02/11/mirroring-multiple-sql-server-databases-on-a-single-instance.aspxThis is a question I get asked a lot by customers (last week being the latest) and the answer really depends on which platform you are running on. There is a support policy in Books Online that states that we only support a maximum of 10 mirrored databasesen-USTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)