In case you don't know, some time ago I started a ruby-on-rails plugin for RightJS called right-rails, which was just updated to the next version 0.3.0
There are actually quite a lot of interesting and fancy stuff going on and it tries to solve many of usual headache of ajax applications development.
Then small things like transparent Prototype/Scriptaculous helpers replacement for RightJS, plus various helpers for the RightJS own features and modules, plus automatic scripts including handler, etc. etc.
If you like RightJS and do ajax stuff in rails, check it out, you'll find many helpful stuff.