Further progress with integrating Professor Tao Ju's dual contouring contribution into Blender.
The video shows various modes and features; in particular note that sharp edges are working now.
At this point the code is only integrated as a mesh modifier, but I'll be looking into the metaball code to see if it can be better integrated there as well. There are also a few features left to enable, as well as some unfinished areas such as better handling for polygons that aren't quads or triangles.
A patch against trunk is available here: