What You Can Create with Stereolithography
Stereolithography allows you to create almost any 3-D shape you can imagine. If you can get it into a CAD program, you can probably create it. The only caveat is the need for structural integrity during the building process. In some cases, you need to add internal bracing to a design so that it does not collapse during the printing or curing phases.

The photo below shows you a typical object that has been created at PT CAM. The piece is lightweight and has the strength of polystyrene plastic. You can mount it, drill it, etc., so you can try it out in actual use. For example, a chair manufacturer will produce different arm rest shapes using stereolithography and try them out on actual chairs to see how they feel.

This is a close-up of an engine manifold:

For more detail on the manifold, see this short video.