I have been playing around with the viewport Ambient Occlusion to make models look nice when walking around with Fly Mode. A nice trick is to crank up the AO strength to 20 and, wind the distance down to 0.05. The outcome is a pretty good edge shader that works in realtime.
Here is a screen shot from a random model grabbed from tf3dm.com, to show you what I mean:
This could be incredibly useful. I can imagine using it to assist with outlining a busy scene composition, where there might be a mess of meshes still lacking materials.