This was the thing that sold me: $ macirb >> ''.class => NSMutableString MacRuby is Obj-C! Of course, this works both ways: some stdlib stuff is current

This was the thing that sold me: $ macirb >> ''.class => NSMutableString MacRuby is Obj-C! Of course, this works both ways: some stdlib stuff is currently less reliable than using the Cocoa framework equivalent. Either way they're making really awesome progress and it's an exciting project to watch.