A couple of really good links for you to learn and hopefully help you:

http://msdn.microsoft.com/en-us/library/ms190030.aspx

http://msdn.microsoft.com/en-us/library/ms189931.aspx

One of the items I watch is the RedoQueueKB. Tells you how much data would need to be applied on the mirror during a failover before the database would come online.

http://msdn.microsoft.com/en-us/library/cc917681.aspx

Hope they help.

Fraggle