Nowhere did I see on the website the resolution of the layers. That is an extremely important variable in the equation, regardless of the scale of the part being rendered.
You had to dig for it, Bryan. Under "Process", it specifies X/Y of 686/in and a Z of 800/in. So the minimum voxel is .0015" x .0015" x .00125". That's pretty good, and means you could spend less time designing around aliasing. The primary limitation I noticed was the resin, which by their admission is fairly brittle. I would conjecture that small N detail parts would be hard-pressed to survive cleanup handling, but it would be quite interesting to try a carbody or loco hood.
I've been following
http://www.shapeways.com, which according to the samples in the gallery, a couple of guys in Europe have been producing carbodies and building details in N. Their machines are still too coarse, IMO, and you would spend a lot of time (and money) tweaking your artwork to the limitations.