I have actually used STL files on a rapid prototype machine at school and they are good to go once you make the final model and export them.
I used a
Z-Corp machine to make some random stuff (robot parts, lego's, a double helix, and a skull among other things.) and then we as a class proved a design from the required text as miserably failing (big surprise) when we made the assembly of a flashlight like this one shown
HERE and the flashlight's handle was too small to fit a human hand in. Oops..