[QUOTE=srealist] I'm curious to know how the shader SDK will work and if we can write our own shaders from scratch in GLSL. Also what version of GLSL is implemented?[/QUOTE]
Effects are just a .xml file with some metadata, and a .fx file with the GLSL code to run. So it's really easy to make new effects.
WebGL is based on OpenGL ES 2.0 which IIRC is comparable to desktop GLSL version 1.2, but not identical. You have to write shaders for the ES variant rather than desktop since that is what WebGL uses.