Earlier tonight I committed a memory-usage reduction for the function used to generate adjacency for the smooth brush in sculpt mode:
r44933 – Reduce poly map memory usage (used by sculpt smooth brush.)
The poly map tells you which polygons use each vertex, information that is not normally available outside of edit mode.
It’s a relatively small amount of memory compared to some of the bigger mesh element/VBO allocations, but for a mesh of 1.5 million quads (non-multires) it reduces the size of the adjacency allocation from 168MB to 48MB (for 64-bit builds.)