Ray Tracing

Goddamn all of these homework threads. Let's talk about something interesting.

I'm starting work on a ray-tracer for shits, /proggles/ Any tips on speed improvements? It's being written in C.
I know the show stopper (usually) is having to check each element in the scene and see if it has been intersected by a casted ray. Any ideas on improvements in that area?

>closer to a model of reality
You can get much closer with OpenGL. tracing rays is the inefficient bruteforce solution.
What if you want to add some effect to your raytracer? That which is not possible in the "pixel reality"? Can you see you prematurely limit yourself to fixed pixel reality of your raytracer(which is pretty primitive compared to full set of openGL effects and transforms)