Changing materials, moving objects around and adding/deleting new objects can be done in real-time and the Cycles rendering engine can also rebuild the acceleration structure of the Suzanne model at lightning fast speeds. The source code will be available in about two weeks! It's going to be really cool when you can modify your model and immediately see the changes rendered in real-time in photoreal quality. Speaking of real-time editing and rendering, one of Luxrender's developers has made an utterly amazing video showing live editing of a physics simulation inside Blender and rendering it in real-time with Luxrender's PathGPU2 (a 100% OpenCL path tracer and part of SmallLuxGPU v1.8 with a heavy focus on animation rendering):
http://www.youtube.com/watch?v=bSQoJW9ajmU (real-time part starts at 1:23)
The video was rendered on a Core i7 920 + 2x ATI HD4890's, certainly not a bad system, but the HD4000 series was not exactly conceived with OpenCL computing in mind. I would love to see a GTX580 rendering this scene though. According to the graph below from Anandtech depicting the performance of SmallLuxGPU 1.7, I can imagine that card would just fly in this scene and make the video that much more awesome!
Update: SmallLuxGPU 1.8beta (which incorporates Metropolis light transport in OpenCL) is now available for download from the Luxrender forum
Update2: A lot of useful information and implementation details on the Cycles renderer can be found on http://wiki.blender.org/index.php/Dev:2.5/Source/Cycles under the header "Design"