I am barely getting a post in for 2010. This is my stake in the ground that this blog is the lamest one in the world that is technically still active. I welcome competition.
Onto a post. I think in 2010 we have reached a quiet revolution: we can do tens of millions of rays per second quite easily, which means we can get 16 rays per pixel in a second, even with global illumination. This means we can do progressive preview "well enough". If I were to do an MS thesis today, it would be on a UI for such systems.
A question for the future is whether batch rendering system architecture will start being determined by what is good preview, rather than preview trying to match batch.