crazy_dave: Out of curiosity, what's the advantage of using the universal extractor (which is Windows only right? so it has to be run in Wine anyway, yes?) over simply running GOG's .exe installer in Wine?
The pros of using Universal Extractor are that it's really, really easy to get at the data files for games like Duke Nukem 3D or Descent/Descent 2 which have open-source ports. You just point it to where the GOG installer is and it spits out a folder with the game's files in it. This also works for GOG games that use DOSBox. Nine times out of ten or so, you can take the folder with the extracted game's files and drop it into Boxer's startup window to import it.
The only problem with this is for games which use DOSBox. As I learned, in some cases (like Wing Commander 1+2, and Little Big Adventure 1/2), the GOG installer creates a custom configuration file which tells DOSBox how and where to mount the virtual disk volumes it needs for the game to work (among other things, like the correct sound settings). Since Universal Extractor circumvents the GOG installer, these settings aren't found and the game doesn't work in Boxer.
I've gotten around this by running the GOG installer in CX/Wineskin, and then getting at the data files for use in Boxer (for CX, go to ~/Library/Application Support/CrossOver/Bottles/<game bottle name>/drive_c/Program Files/GOG.com/<game install folder>).
Oh, and as a PS, I've updated my GOG mix with the latest Windows games I've gotten to work; as before it's at
http://www.gog.com/en/mix/mac_friendly_gog_games_4. It's extremely tedious to move all of my latest entries up to the top, so they're all at the bottom of the list...