http://www.blender.org/development/release-logs/blender-250/sculpt-and-multiresolution/
Release logs are work in progress, also check missing items on that
page, there's still a few things that need work.
Quick summary of the changes:
* Use BVH for optimizing sculpt mode, doing only editing and updates
on nearby nodes.
* Memory reduction by use of CCG grids for subsurf, own undo stack,
no vertex-face map, no origindex, .. .
* Multithreading for sculpting, multires, and subsurf.
* Optional external file storage for multires displacements.
* Various tweaks to brush behavior.
71a43e2069