The new Saab-Hummer-Cadillac here in Pittsburgh is very nice. It's all in one building with 3 different "faces" angling away from each other but connected in back via a common "service and delivery" area.
The Cadillac store is all glass and stainless steel. Very modern, very chic. It has giant.. and I mean large enough to drive a lifted Escalade through, set dual sliding glass doors that woosh open in a Star Trek like fashion as you walk up to them. It's relatively small inside compared to most of the mega dealers you see, but easily the classiest I've been in.
The Saab store is like walking into Sweden. It's basically an IKEA catalog store. Very attractive if that's your thing... and for most Saab customers, I expect it is.
The Hummer store looks ruggadized and old school industrial. I've never bothered to go inside, but there is a pile of rocks out front with a Hummer parked with one or two wheels on it.
In the center of the building is a delivery and quick service area. It's open, airy, and glassy. Lots of natural light. The few times I've been in there it has been positively spotless. There is nearly always a car sitting in there waiting for it's new owners.
Each of the individual stores feels small... like a boutique. I'm sure that is on purpose.
Overall, if GM replicates this setup country wide, I'm sure they will do well.