I've had my eye on deferred lighting for a while. In my renderer, I've tried sending an arbitrary amount of lights through a shader and using expensive loops per-pixel, and an attempt at forward rendering that requires me to draw the screen a bunch of times which is also very expensive.
However, it sounds like deferred lighting still requires a forward renderer for transparent, reflective, or refractive objects. Is that correct? I could understand if this is the case for transparent objects, but not for reflective/refractive objects since you could just render the scene to a cube map with deferred lighting applied to it. Also, if I'm wrong and reflection and refraction is possible, then why not just make all transparent objects refractive with a refraction index of 1? Sure, cube maps can be expensive, but then again, everything is at least a little refractive. It could us to abuse refraction and reflection more since the maps are updated anyway.
Now, here's the biggest problem I face: all of these are pretty tough on mobile hardware. MRTs won't be an option on mobile hardware until Open GL ES 3.0-compliant devices are mainstream since Tegra 3's the only hardware I know of that support it as an extension... My shaders for mobile allow you to have up to 1 of each light enabled: global (directional), point, and spot light, but that's quite a bit too. Would supporting light maps be the best way to go for mobile devices?