We do 3D printing from sketchup architectural models to a local reprographics shop here in Seattle. They have two options: 1) send them the SKP file and let their technicians tweak it into printable format, or, 2) use an STL (http://rpdrc.ic.polyu.edu.hk/old_files/stl_introduction.htm) conversion plug-in in SU to generate the file ourselves.

3D printers require STL files to print. Sketchup doesn't do this natively, and any conversion can take a lot of tweaking to get right.

On the plus side, the new 3D printers do color and can print your materials and textures directly into the model matrix. You can also create true moving parts if you model the thing in such a way that the pieces are not contiguous.