Hello,
I don't really know who I should tell this to, but I was searching the Codex about JOIN in SQL, to find a way to grab posts from 2 custom types at once using a join, when my finger slipped on the keyboard and I searchd for "joint" instead (don't ask me why...)
Well, here are the results: http://wordpress.org/search/joint?documentation=1
I thought someone should know about it.
Best
Paolo