Excellent plugin! I've used it on WP on Apache before with no problem. Now I'm sitting behing Nginx, and when I try 'Force SSL' I get an infinite 301 redirect loop. The page in question is here.
If I uncheck the 'Force SSL' options and specify https:// in the address bar, the resource won't redirect and the the ssl connection is honored (albeit without the internal URL rewriting but hey, does that help?)
I looked at your code, daunting but I don't have your insight. Can you point me in the write (I kill me!) direction?