I am running 2.3.11 with RubyGems 1.7.2 without having to require a "thread" or make any changes to existing Rails code. The 1.8 series is causing problems for me, so I downgraded.
gem uninstall rubygems-update
gem install rubygems-update -v 1.7.2
update_rubygems
gem -v
=> 1.7.2
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