I just posted a quick description of Sketchfab’s new interactive WebGL material editor on my personal blog. You can find the post here:
Even if you don’t use Sketchfab to publish your 3D models, it is actually quite useful to just upload a generic model and experiment with the material editor’s parameters. These are the same parameters that come up when you work in a rendering software’s material editor. Using Sketchfab’s editor, you can interactively change them and see what happens.