On the user forum, I've often seen questions like this:
"- Can I trace which rules are executed with what bounded variables and in which order"

Debugging in the IDE's doesn't cut it (eclipse plugin is borked and intellij/netbeans doesn't support debugging DRL).

Instead something like this in the code would help:

if (logger.isTraceEnabled() { // returns immediately => NO NOTICEABLE PERFORMANCE DELAY IN NON-TRACE MODE
    List<...> boundedVariables = ...; // Retrieve bounded variables only in TRACE mode
    logger.trace("  Rule fired with name ({}) and boundedVariables ({})", ruleName, boundedVariables)
}

Then the user just has to do this in his logback.xml (or similar in log4j.xml):

  <logger name="org.drools" level="trace"/>