Ruby, unlike Java, has full native continuations and call/cc ala LISP. This makes for some really interesting code, mind-bending and very rewarding. For web programming, it moves you away from a messaging model to more traditional program flow: you get to code linearly, but the program is still multiplexed in the web way.
There is a great future for futures.
(I had trouble with the link. A bright spark suggested the wayback machine.)