For anyone interested, there's now a port of memcacheDB using OpenLDAP's MDB (memory-mapped database) available on https://gitorious.org/mdb/memcachedb in the branch "mine" (the master branch is just an import of the original memcachedb code from SVN).
MDB is several times faster than BerkeleyDB for reads, and has a much smaller footprint. You can read more about MDB here: http://highlandsun.com/hyc/mdb/
