I have a really nice looking crystal material using cycles applied to my object; it's pretty fast and very simple - Just one glass node. Is there any way to convert this into an HLSL shader for use wihthin Unity? My understanding is that cycles materials are left out when Blender files are used in Unity.
I don't think that is possible, at least the results will look different. Cycles uses a completely different rendering system than what realtime graphics applications like Unity use.
The Cycles Renderer is a ray tracer and has full knowledge of the whole scene all the time. It can model shadows, reflections, refractions and indirect lighting pretty easily, but they cost a lot of computation power.
Unity on the other hand uses OpenGL and Direct3D for rendering. Both APIs are optimized for realtime graphics, but during rendering only single objects are known. Reflections and shadows have to be faked by rendering the scene multiple times from different angles. To get performant global illumination it is precalculated and refractions are usually faked by distorting the final image.
You could approach this in a way that I have found relatively decent although it doesn't necessarily achieve the complete result of a cycles material. What you could do is:
What this will accomplish is a model with a diffuse material, but a baked "texture" (UV mapped) version of your material.
If you have a complex or semi translucent material then this becomes a bit problematic. As others have mentioned, the raytracing render method that blender uses is far different from the realtime materials used in unity. You have to fake things like reflections and translucency when you bake textures in blender and then transfer them to unity.
But if you want a basic texture based off your material, you can accomplish that with the method above.