a good idea came into my mind: a Refraction-Node. The node could use the normal-output of a render-layer-node to alter the matrix of a second (background-)image, as if it were distorted like a refraction.
The good points would be: it wouldn’t use raytracing, like that, you can make dof and vector-blur behind refracted glass.
The bad points: because it can just take the camera-facing-normals, it weren’t like real refractions.
I know, it’s easyly said, but (perhaps) hard to code… I wish (like a lot of blender-users) i could code, but i can’t… ))-: …it’s just a good idea.
Maybe it’s also useful for Reflections??