It has been confirmed from a poster on the beta forum that mouse do work on the PS3, also I by pressing R1+L3 a mouse icon appears on screen for ease of use.
I found that little R1+L3 "mouse mode" Icon to be the opposite of easy to use. An actual USB mouse is far superior.
I'm still crossing my fingers for the PC User Interface (not the crossbar) to be available as an option for PS3 users.
Also, if the text command /nextenemy is implemented, then you would be able to create a User Macro and map it to the Cross-bar. During P3, the PS3 really needed a way to easily select/switch targets during battle. I think this is essential, and I just can't see how it would possibly be overlooked in P4 and release.