SQL Server 2005 - Database Mirroring off the cards for RTM.
So, Database Mirroring will not be "on" in SQL Server 2005 when it releases.
From what I have read, it looks like it is not performing up to expectations. You can still enable it, but it's probably going to be one of those "we told you so" scenarios.
I do not doubt that it is robust and won't trash your data, but I do think it is a bit too slow for production use.
I just thought it was the June CTP that made it slow. I have not been able to crash it yet.
Paragraph 5.1.2 from the September CTP shows how to enable it
http://download.microsoft.com/download/9/7/e/97e4c6e8-18e6-4c61-b1df-bdf4a66b146b/ReadmeSQL2005.htm
The updated letter from Paul Flessner's really raises the point
http://www.microsoft.com/sql/2005/productinfo/letter.mspx
Pity, my presentation for this Wednesday at SQLCon 05 in Germany has just been blown out the water.