Sculpt mode in Blender has been optimized, increasing drawing and editing performance, and reducing memory usage to support more detailed models. New tools have been added and existing ones improved. Multiresolution meshes have also been rewritten, now available as a modifier to integrate better with the animation system, and preserving displacements when editing the mesh topology.
While sculpting, meshes are now internally split into smaller parts, for quicker editing of local parts of the mesh. Sculpting, multiresolution and subdivision surfaces have also been fully multithreaded.
Drawing speed is drastically improved by keeping the mesh on the GPU, and for very detailed multiresolution meshes it is now possible to show the low resolution while navigating the view.
Memory usage has been reduced by a factor of 2-4x, and more when storing multiresolution displacements externally, which permits each individual object to have as much detail as fits in memory.
Multiresolution is now a modifier, much like the Subdivision Surface modifier. This means it can be placed after for example an armature modifier, as is typical for animation, and the displacement will follow the deformation. A restriction is that it can't be placed after a modifier that changes the mesh topology, for example a mirror modifier.
Multiresolution displacements can now be stored outside of the .blend file. This helps keep the .blend file small, and makes it possible to load the displacements in memory only when needed.
This can be considered much like a displacement texture map that only applies to a particular mesh, and that you might store as boots_disp.btx next to a boots_color.png, for example. Saving to this file happens automatically when saving the .blend file. For performance, you can ensure that it does not get loaded into memory when opening the .blend file, by setting the viewport level to 0 in the multires modifier.
New is the Clay brush [more info].
Things are still under development, and a few things are missing:
Sculpting with modifiers enabled can have an impact on performance, and may give intuitive results in some cases, so it's good to verify how they are set up while sculpting. In general it's best to have the multires modifier last in the stack, and when sculpting the base mesh to disable modifiers.