Lord Odin is showing the impact of some recent Cycles developments that have sped it up to close to real-time.

Thanks to lukas stockner and a few of the main cycles devs cycles has become 10x faster or 10x cleaner.. We can denoise, We can blend between noise, We can even remove the randomness (noise) from the sampling to get clean renders from the first sample, We can switch to AO after a certain number of bounces. We can limit texture size to fit our previews in to vram.. We can hide geometry far away, We can hide geometry behind the camera, We dont sample lights that we cant see, We dont sample lights that are too weak to contribute to the scene, We do a lot of things apparently.. Who is "we" IDK what im talking about its 3 am..

More information is available on BlenderArtists.

If you want to try this out for yourself you can grab an experimental build (no Linux support - yet), and download the classroom demo file from Blender.org. Please do share your results - did you manage to get the same kind of speedup?