Please update app-emacs/ruby-mode to the current ruby-version (1.8.4.20060226).
Thanks for the note. I updated it to ruby-1.8.4.ebuild, which isn't quite what you asked for. The Emacs Herd has contacted the Ruby Herd. We're hoping to merge app-emacs/ruby-mode into dev-lang/ruby so that the Emacs mode and Ruby versions will always be in sync.