Sadly I need to work with a rails 2.3.3 and 1.2.3 app now and then and the latest rubygems has issues with these old versions of rails. For example:
rake my:task:name
rake/rdoctask is deprecated. Use rdoc/task instead (in RDoc 2.4.2+)
rake aborted!
uninitialized constant ActiveSupport::Dependencies::Mutex
So I have to downgrade. Not a huge deal. I'm now using rbenv
gem update --system 1.4.2