What works what does not and may not

I have just forked ruby-processing and updated my fork to match work in progress on my linux box to get ruby-processing running with the latest jruby-1.7.1 and latest processing-2.0b7 release. https://github.com/monkstone/ruby-processing clone it if you like. All samples should work, with the exception of the peasycam sketch (does work with an unofficially updated version of peasycam). Examples that rely on external "contributed" libraries probably will not work with the probable exception of toxiclibs (which is implementation agnostic). I don't think control panel likes working the latest version of processing (it was ok with processing-2.0b6).
Since web applets are no-longer supported with vanilla processing I don't think there's much call for it in ruby processing. For web presence with processing you are encouraged to write processing.js sketches (there is even preliminary support for coffeescript in processing ide). I have requested that my modified fork is pulled into core, which will make it easier to use but in the meantime you can clone it from github or fork it if you've a burning desire to implement something new.