I've created a super simple example application using Macruby. The problem is that the prefpane won't work, nothing happens.
I've created a button, that has a callback in the Main.rb file. When someone clicks on the button the label should change value to "Some data".
The link to the Main.rb file also contains the non working example project.
There is only 3 lines of code added.
The problems were being shown in your console messages (Console.app). Or if you would start System Preferences.app from the command-line you could have seen the messages there. Anyways, copy-pasting from the commit message:
Last but not least, since MacRuby is still a ‘young’ project, I urge people to ask their questions there, so the actual community can help out.