Wanting to swap one of the two stock hard drives for an SSD (OCZ Vertex 3)
Followed the standard Mac Mini hard drive replacement guide - Installing Mac Mini Mid 2011 Hard Drive Replacement. Worked perfectly using the 26 Piece Bit Driver Kit, Mac Mini Logic Board Removal Tool and Spudger from ifixit.
Followed the instructions as per the guide - only one slight change was to step 12 - need to remove both the hard drive connectors. The top hard drive as you view the Mac Mini in the upside down position (with the left hand connector) is the boot drive.