Hi,
I suspect that experiences will be different for every modeler, but I have been experimenting with my 3D printer for use in model building for a while and have found it very useful.
In general, especially since my printer is a relatively low end model, I have been viewing mine more as a tool for helping me scratch build a model rather than as a tool to make exact scale replicas. But since its my understanding that even with output from places like Shapeways you may still need to do a bit of "post processing" and clean up, I suspect that stuff from sites like that may fall at least a little bit into the category of being a "starting point for additional work" rather than an "ready to use end product" for many modelers anyway.
Anyway, here are a couple images for a new project that I started working on recently. Here I have taken a 3D computer model for a "What-If" ship that I drew up on my computer and broken it into several smaller sections for printing, that I intend to "clean up", "join together", and then do some extra work on to make a ~1/300 scale model of my ship.
In the images above you can see that everything did not come out perfect, and I'll need to do a little clean up, filing, sanding, and putty work (which I have already started on the two small lifeboats in the bottom picture), but the piec es have come out fairly well and there is a lot of detail in things like the mast, the built in inclined stairways in the stern section, etc.
In addition, I was also able to make the bulkheads around the open qurter deck fairly thin but still relatively strong.
By doing this on my own 3D printer I've been able to play around with different ideas on how to best break the ship up into smaller sections, and lay these sections out to try and minimize wastage and limit the areas where a lot of cleaning might otherwise be required, and in general make the parts for a relatively largish model (~10.5 x 2 x 2.5"). Specifically, I made the bow in two pieces, split along the centerline, so that I wouldn't have to print alot of temporary supports to help when printing the bow flare.
In addition the stern was made in several pieces for similar reasons. For the mid section I was able to cut away alot of the interior of the piece leaving only a "mostly" solid shell and some internal cross bracing. Since I've taken these images I've also printed out most of the focsle deck, with cut outs for the main windows as well.
Anyway, hopefully these images help show some of what can be accomplished even with a fairly basic 3D printer, and how you can either make a full model or just parts, for scratch building etc.
Pat