I've been trying to recreate the issues that you guys have been having with hybrid rendering and just can't seem to do it.  Hardware setup on this box is an fx8150 and ati hd7750.  I just click on gpu rendering.  Collect textures and full size is on and it just works.  SLG works so well that I use it almost exclusively for test renders.  I think from what everyone has posted that it doesn't seem to be a hardware issue; so, there has to be something in the scene itself, or lighting, or materials that is making gpu rendering puke it back at you.