0.5 is the only Mac version, and is not currently supported. It does not have any plugin support and as such you can't configure the controls. The default controls, however, are listed in the application's readme file (and I have pasted them below). As for saving, there is no save state support. And as far as I can tell, the program is incompatible with either Leopard or Intel Mac's as mine crashes after a few seconds no matter what game I'm loading.
Configuration in general leaves a lot to be desired. Only other tip I have is if you want to change the fullscreen resolution, you need to do it in /Users/Username/Library/Preferences/com.emuscene.Mupen64.plist
I've already asked for an update, but the current developers don't have much experience with porting/compiling for OS X. I tried looking into it myself, but some of the libraries are particularly difficult set up on OS X and I gave up as I'm obviously just not up to the task. As such, it's unlikely we will ever see an update unless some interested Mac developer crawls out of the woodwork.
Game-Play Controls:
R_DPAD = KP6
L_DPAD = KP4
D_DPAD = KP2
U_DPAD = KP8
START_BUTTON = RETURN
Z_TRIGGER = SPACE
B_BUTTON = X
A_BUTTON = Z
R_CBUTTON = PGDWN
L_CBUTTON = DELTE
D_CBUTTON = END
U_CBUTTON = HOME
R_TRIGGER= S
L_TRIGGER = A
