I've been a smart owner via the smart center in Buffalo, NY for about 7 months now. Having one of the first cars off their first delivery, I've had ample time (and too many visits) to the center, and know the staff there pretty well.
The smart center itself is great. They staff are helpful, and know all about the cars. They keep up with things (a few actually read here), and hosted a rally just this past October. The finance group is decent, and they're doing ok from what I hear.
The smart service center on the other hand truly sucks. They share their service center with the linked Mercedes dealership, and only have a couple of mechanics that are trained on the smarts. Their service center lead has changed at least twice in the 7 months I've owned my smart, probably because of customer complaints.
In the 4 visits I've had here, none has lasted less than 5 hours, despite the "repairs" being needed being very small. Keep in mind, the service center is over an hour and a half away from me, and does not have weekend hours. They're open from 8am to 5pm, Monday through Friday.
In one instance I brought the car in after the O2 sensor threw an engine code. I called ahead of time, and emailed their service lead with the error code and the part number for the O2 sensor, since the forums here were rife with reports of the same code and failed part. I was assured they'd have the part in stock to do the repair. It was the only thing I was bringing the car in for. When I arrived (two weeks later), they held the car for 5 hours, and then came out and said they didn't have the part and needed to order it.
So, the basic summary: The smart center itself is great, but if you plan on getting service done there, don't rely on them having things you need. It kind of sucks, since in some cases they're the only option, since anything involving servicing the on-board computer can ONLY be done at a smart service center.