For me, one of the real benefits so far is getting me back into the C world... I've been away for some time doing Java mostly so it's fun to get back into the swing of things.
I've just recently found the YARV project. From what I have seen so far, it appears to be working toward a multi-threaded version of Ruby which makes me very happy! Ruby is a very cool language and serves a good purpose. Rails is wonderful for getting things off the ground soo quickly... but in today's web world, non-thread safe languages pose a few barriers.
These barriers can definately be overcome (and are everyday) but the web is a multi-threaded world... if YARV does push Ruby into the MT way of things, I think it will only serve to boost the already crazy swirl surrounding the Ruby/Rails phenomenon.