Hey guys,

 I felt the need to dive into an old Apple sample to understand how to do some advance window manipulation: http://developer.apple.com/samplecode/RoundTransparentWindow/index.html

Porting the sample to MacRuby was pretty straight forward :)
http://github.com/mattetti/macruby-roundtransparentwindow/tree/master

Laurent, feel free to change the license and provide the example with MacRuby if you think that could help other developers.

- Matt