I have attempted to contact the author via his own site about these matters, but received no answer.
My problem is simple: I disabled Efficient Related Posts in order to diagnose a slowdown in which my home page (at http://www.technightowl.com) takes 10 seconds to display. This problem is repeatable after clearing the browser cache. None of my other sites have the problem, and I am on a dedicated server with high memory/powerful dual quad-core processors/huge RAID drives.
When reenabling the plugin, the WP Admin page just timed out. Note that my PHP and MySQL settings call for longer wait times, so that shouldn't be an issue.
But I also determined that Efficient Related Posts was the cause of the slowdown.
I am using another plugin with similar capabilities, Contextual Related Posts; there's no more slowdown, but it uses twice as many database queries. I'd rather go back, but I need some guidance to solve the problems.