Good thread.  I used to get all upset because I couldn't get a render to ever come out right.  didn't know as much then, though.  However, now that we have a way to get a scene to Luxrender, I actually kinda like Firefly.  I can usually have a decent quality render in less than two minutes, IDL included (cheating a little bit though, I got a six-core Phenom just for this purpose).  While the renders are nowhere near unbiased quality, they actually turn out really well considering that, and I love not having to wait fifteen minutes before I even have a clue what it is going to look like.  I can use it for a preview then let Lux churn out the final.

Now that Firefly has IDL support, plus D3D's Render Firefly script, I think the only thing missing is a little more physics in it.  I would like to see the light do some bending around objects (like real light), I think that would really add to the realism.  I expect that would be a pretty big change to the renderer and don't think it will be implemented because of cost factor for SM's target customer base, but just thought I would mention it.