I thought I should probably mention over here that I just added another article to JCSref:
Event Theory
This article obsolesces all previous articles describing the manufacture of MCEs, including my earlier "MCE's - why and how," although it does rely on existing MCE and Ambient Sound lists. Basically, it's everything I know about MCEs. This article starts from the bottom up and explains JJ2 code, SCEs, crates, and standard and expanded MCEs. By the end you should be able to generate trigger crates of any TriggerID, create a steady stream of big rocks going along a belt, use gun crates in multiplayer safely, or just have any number of things repeatedly fall from the ceiling. It's pretty cool stuff.
(Thanks to Cooba and plunK for beta reading... since then, I've added illustrations, a brief mention of MCE stacking, and a more detailed/helpful final section.)