I'd like to apologize in advance if I am reiterating points made earlier;but I didn't want to read EVERY post on ALL five pages.
Just to chime in with my two cents REALLY, REALLY late, I have been experimenting with different front-ends on my PC recently to see what is available out there on this front.
My impressions so far have been mixed.
One great front-end from a "configuring games per ROM" stand-point is Arcade.exe.
This program allows you to set virtually ALL your settings per game by right-clicking the name of the game in the GUI.
The program edits the config files for each game, allowing you to do per game rotation, alter the resolution for a specific game only, etc...
My only complaints about this one are that it leaves the desktop viewable around the edges unless the screen resolution is set really low, and the fact that you can't create custom skins for it.
The front-end that has most intrigued me in my search, and will be going into my current cab when the new cab for my Mac gets done, is MAMEWAH.
THAT one is absolutely awesome from a GUI configurability standpoint.
Its strongest point is the fact that it includes a "layout designer", which you can use to create your own custom layouts.
You insert your own background graphic, and then overlay it with boxes for screenshots, marquees, game info, etc...
Using this, the front-end truly becomes YOURS.
YOU pick what background you want, and YOU pick what info to display, and where.
It also allows you to create custom game sets automatically by screen orientation, controller type, year, manufacturer, how often you play the game, etc...
You can also edit your own lists, to show only the games YOU want in a list, as well.
Another of its strong points is that it will allow you to run multiple emulators from the single UI, and will even customize the skins/layouts for each emulator.
It is not as robust as Arcade.exe in allowing you to customize individual games, but makes up for that in visual appeal.
The thing I like most about MAMEWAH though, is that it was designed from the ground up to work seemlessly in a cabinet.
The UI on it uses "1" as the enter key, and "2" as the select key.
With the addition of a joystick for navigating menus, everything is accessible--even on a single 4-way joystick w/two start buttons cabinet.
This allows you to create a kiosk effect once the program is running, that will prevent people from "accidentally" messing things up.
THAT is where I would like to see this project go.
The Mac community as a whole has always been about "make it your own".
I would really like to see that idea work its way into this custom front-end idea.