What I gather it does is cache pages to reduce access time on the database. I don't personally see how it would work because a forum is dynamic. That is, if no-one posted, sure you could cache pages. Once someone makes a post, surely the whole page (and indeed the thread list) has to be remade?
I think it might account for why sometimes a page loads in one second (the cache?) and at other times takes 15 seconds (the database?). Just a guess.
Whatever nginx does (and I understood it to be an alternative to Apache), caching at the server is only of benefit if the server is dog-slow as each instance has to traverse the whole Internet. Caching by your ISP on the other hand, if it is practical, is extremely effective.
I briefly thought such utter garbage as the insane "token" redirect (or indeed, any redirect whatsoever) in particular, and likewise, that "You are Already Logged In" had been fixed.
OK. I was quite wrong - though it is just a little better.
Kudos - the "Broken" page does seem to have departed to its unholy father.