How to Submit a Material
This guide will take you through the steps required to submit your material to my Testing Library.
The first thing you'll need once you've got a cool material you'd like to submit (be sure it's your own work!) is my material library add-on for Blender. To install it, download the .zip file, open Blender's user preferences, and install the downloaded .zip file from the add-ons section.
Converting your Material
Once you have the add-on installed, make sure you're using Cycles, then go the material settings in the Properties window. You should now see the Online Material Library panel; go to the add-on's import-export tools.
Select the Blender text datablock you'd like to write to (or leave it as the default, 'bcm_file'), then click the "Write to Text" button. Open up a text window in Blender, and select the text datablock you wrote the material data to. Assuming your material has no images (otherwise, read below), all you'll need to do is copy the .bcm code and paste it in the material submission form.
Once you have the .bcm code, just
- Enter a name for your material
- Select the category which fits it best
- Enter your name if you wish to be credited
- Enter your e-mail (never shown) if you wish to be notified when your material is moderated
- Confirm that the material is your own work and agree to license it as Creative Commons Zero
If your material doesn't use OSL scripts, nodegroups, or image textures, that's all you need to do. Click the big ol' Submit Material button and you're done!
Material Previews
This step is not necessary, but it's not a bad idea to submit your material along with a link to a preview image.
Doing so mainly helps us to get a good idea of what your material should look like when set up properly (but may also result in your material being moderated more quickly 
).
The preview image can be a render of your material in your own scene, but you may wish to use the B.M.P.S. (Blender Material Preview Scene) created by Robin "tuqueque" Marín, or the official Cycles material preview scene built into Blender. Whatever one you choose, make sure that your material is clearly visible, and mapped to the preview object well.
As far as resolutions go, 256 x 256 is a good size for your preview image, but other sizes are okay too. If you need hosting for your preview image, try PasteAll.
Image Textures
If your material uses image textures, you'll similarly need to upload them somewhere on the web and provide links to them on the sumbission form. Any resolution is acceptable.
You are allowed to submit a maximum of three (3) image textures with your material. The images must either be your own, or licensed as Creative Commons Zero.
Once again, if you need hosting for your images, PasteAll is a good option.
Nodegroups
If you just export your material to a text datablock with the "Write to Text" button as described above, the nodegroups are automatically embedded in the .bcm code. You won't need to do anything extra.
However, if you export your material with the save button instead, you'll need to disable the option "Write nodegroups to separate files" in the Add-on settings to get the add-on to embed nodegroups in the .bcm file when exporting.
OSL Scripts
If your material uses OSL scripts, right now your only option is export your material with the "Write to Text" option. Otherwise the .bcm code will only contain a link to the .osl or .oso file on your hard drive.
It is highly preferably to submit the .osl source code for scripts rather than the compiled .oso code. As with image textures, be sure that any OSL scripts you submit are either your own, or licensed as Creative Commons Zero.
That's all -- happy Blending! Feel free to submit any cool materials you create.