Looking at the reference it seems that it has been updated for Processing 2.0 already, for example see the shaders section. Not sure if it's completely up to date yet though. Apart from that, there is no elaborate documentation yet, because Processing 2.0 isn't out yet. It's still in beta, being developed and changed. Once it out, more helpful resources are likely to appear. For now a good source of information is andres' blog, although some of that information is probably outdated due to changes in the newer beta's. Also when you post specific questions about the 2.0 opengl functionality, andres often comes the rescue.

Since there are many differences between the GLGraphics library and Processing 2.0's opengl functionality, using those resources isn't a great reference. However if you want to get some experience with opengl/glsl in a more documented and stable environment then 1.5.1 + GLGraphics 1.0.0 is still a good alternative.