Light Cache for GI!
The best biased render (Vray-FinalRender) now use this GI algorithm.
It's fast to set up,almost view-indipendent, converge to a physical result, evaluates glossy and refraction, and not only opaque bodies like Importons (that are also more complex to set up). Light cache is the best choice!
I think it's not so difficult, iRay uses an approach very similar to the light cache