No.  From Matt Aimonetti's blog:<p>"Unfortunately, the current answer is: no. The two issues with the IPhone/iP*d OS are the lack of Garbage Collector and support for BridgeSupport (needed to define CocoaTouch constants available from MacRuby)."<p><a href="http://merbist.com/2010/01/31/macruby-0-5-final-is-out/" rel="nofollow">http://merbist.com/2010/01/31/macruby-0-5-final-is-out/</a>