I've just done some O9 skips chassis where everything is 3-d printed - including the wheels and axles.
They run quite well, although not as well as ones with metal wheels and they are VERY light.
The main advantage is it's easy to produce wheels in different styles and size. these ones where done with 20mm axles so these chassis could be used in any gauge between 9mm and 14mm
I've tried this before and had problems with the axle length being made wrongly but this time Shapeways got it right .
This is the wheel in detail - it's in dyed WSF, so nylon and very strong.
To know the meaning of life you need not to be dealt a good hand, but rather to play the worthless hand you have been dealt to the best of your ability.