I just uploaded a dae file I made in sketchup, and noticed that a few outward faces were not the same as the rest of the model. I know you can reverse faces in sketchup, but is that necessary for 3d printing?
Yes, it is best practice to orient all faces before uploading. Shapeways has an excellent internal tool for fixing meshes that may take care of the problem, but why risk it? Its simple in Sketchup....just right click a correctly oriented face and choose "Orient Faces". If you use a Sketchup file for printing on a home printer or just about anywhere else, you will need to orient the faces correctly, so its best to just get in the habit.
Creating a nice looking model is an art. Creating one to print takes it to a higher scale.Give it love, lol.