For the performance-minded, I wrote an article on OpenLDAP for Linux-Magazin's Performance and Tuning book, which was just published. You can download the Table of Contents here:

http://www.linux-magazin.de/technical_review/ltr08_performance_und_tuning

The article summarizes some of the tuning work we've done from ~2005 to the current 2.4 release. (Despite the German publisher, I wrote the article in English.)