The waits are long to get your car repaired, the service staff is medocire, but at least it's a BMW service center and they have really awesome loaner cars when they can't fix what is wrong with your car.
The repair shop is pretty much the only BMW service center located in the penninsula area. The closest other BMW shop is Peter Pan BMW in San mateo or Stevens Creek BMW in San Jose.
The service staff is hit or miss. I've brought my car in several times to Allison BMW and either had incredible service and they fixed the issue with my car right away, or horribly incompetent service, where it took them a week to find a small part and that didn't even fix the problem. Consistency is hard to find at this place.
Allison BMW is located on El Camino Real near the Highway 85 exit in mountain view.