Currently, QtRuby is maintained (if at all) as part of Korundum. Binary packages (for Debian, Fedora, ...) are stuck at Ruby 1.8. The source release qt4-qtruby-2.2.0 of December 2011 supports Ruby 1.9 as well as 1.8.
A third-party implementation, named "qtbindings" in the Rubygems repository, has been made due to the lack of active development. Goals of the project include keeping an up-to-date version of the Qt framework for Ruby, as well as improving compatibility with Unix-like systems. As of December 2013, it supports Ruby 2.0 and 1.9, but not 1.8.