VEXed I am of late...

VEX (Vector Expression) is an internal expression language in Houdini which can be used to develop custom shaders and other stuff. VEX puts a lot of power in the user's hands and is one of the reasons why Houdini is such a flexible and powerful tool for VFX and CG work.

I've only begun to play around with it for a couple of days, but I was already able to implement a Lightwave style fog shader (linear and exponential fog) complete with a simple user-interface in a VOP (VEX operator) network, mostly through experimentation.

Now that I got a taste of things procedural, I just have to dive deeper. I got my hands on "Texturing & Modeling: A Procedural Approach" by David S. Ebert et al. from the school library and will be reading it every chance I get.