Lynn Pettis (2/16/2013)
No additional licensing is needed to use mirroring unless you are using the mirror databases for offloading reporting using database snapshots. In that case the server hosting the mirror databases does need to have licensed version of SQL Server.
While this is true, you'll need the Enterprise edition of SQL Server, if you plan to use asynchronous (High-Performance Mode) database mirroring. Only synchronous (High-Safety Mode) is supported in the Standard edition.