Just FYI, I'll be giving a talk on MDB, OpenLDAP's new memory-mapped database library, at LinuxCon in San Diego next month.
http://events.linuxfoundation.org/events/linuxcon/schedule
Some of the benchmark data I posted here will be part of that talk:
http://highlandsun.com/hyc/mdb/microbench/
If you haven't looked into MDB yet, here's your chance to find out all about it!