Is (or will be) there any sort of light linking in Cycles, or a method to get a light to affect only certain objects that doesn't involve compositing two or more different render layers? Sort of what 3Dstudio does with the Include/Exclude methods.
In blender Internal you have 'light groups' specific for this purpose. Unfortunately, in Cycles this option is still on the ToDo list. If you want to do this you'll need some compositing.
I made a small example:
- Be sure to set 'exclude' layers.
- For the ground plane i used a separate render layer with no exclude options so the drop shadow comes from both lamps.
- Check the 'transparent' option in the 'film' pane of the render setting. Otherwise the background is rendered as a solid color, defined in the world settings.
This is unfortunately not yet possible in Cycles; It is, however, in the To Do list.
It can be done rather easily in Blender Internal, though;