Our robot uses a not small number of 3d printed parts. These include a custom wheel for extending a tape measure, intake rollers, bearing blocks, various spacers and belt drive pulleys (3d printed version of these:
http://www.andymark.com/product-p/am-2813.htm). All of this stuff was printed in yellow ABS plastic.
In case you are worried about our belt drive pulleys being on our drive train, so far we haven't had a single issue with them, even without being solid infill.