I've been thinking about doing this for a long time, but finally got fed-up enough with coffee taking up food space in the freezer. It's a cute 1.8 cubic foot (probably about a quarter albatross for those using the metric system) little cooler-style fridge/freezer. Justified it further since if I ever needed to it has a 12v dc adapter for car use (doubt I ever will). It does feel pretty special for the coffee to have its own storage unit, and it makes finding frozen fruits and meat in the standard freezer easier to sift through. A couple of times I even threw stuff out of the freezer to make room for coffee, so I knew it was time to try this.
Most 12v car fridges use a proper compressor these days. It's still likely very inefficient as compared to a home fridge of course, but due to lack of insulation and inefficiencies of a small refrigerant system.