Crap, seems that somewhere between SDLMame 0117 and 0122 (I suspect 0121), launching games through applescript has broken. An apple script command run in Script Editor:
do shell script “/Applications/MAME/mame0122 /Applications/MAME/roms/game.zip”
is no longer equivalent to
/Applications/MAME/mame0122 /Applications/MAME/roms/frogger.zip
run in the terminal.
For now I suggest sticking with SDLMame 0116 or using MAME OS X with EMUlaunch.

A host of bug fixes and new additions have been made to EMUlaunch 1.5.1. Most noticeably, EMUlaunch now supports screenshots created by MAME OS X. By default, EMUlaunch looks for the nameoftherom.png inside of the user selected screenshots folder. Now if it does not find it it will now also check ~/Library/Application Support/MAME OS X/Screenshots/romname/0000.png. [...]