Contrary to my earlier post about ruby 1.9 going stable, we've decided to add ruby19 to the default RUBY_TARGETS now, rather than wait a few weeks. The main reason for this is that some packages correctly depend on dev-lang/ruby, and thus pull in ruby 1.9 now that it is stable, but they also pull in supporting packages that need to be installed for ruby 1.9. Without the ruby19 target portage will complain that it lacks the ruby_targets_ruby19 USE flag for these packages and it suggests to add them to package.use.
Technically this is correct, since RUBY_TARGETS=ruby19 will be expanded automatically to the ruby_targets_ruby19 USE flag, but it is not a very practical or user-friendly solution. This is why we have decided to add ruby19 to RUBY_TARGETS now, so that things will work out of the box. The ¨downside¨ of this is that more people will get ruby 1.9 pulled in now, and that packages will be installed by default for both ruby 1.8 and ruby 1.9. This was our intention anyway, since it will make switching to ruby 1.9 as the default ruby implementation easier down the line.
Our recommended setup is to not specify anything yourself, so if you already added the USE flags or modified RUBY_TARGETS yourself, we recommend that you remove these again since the default should now work correctly again. By using the defaults you'll make it easier to keep things working out of the box in the future. Obviously, if you care in some way, you can make all these changes!
Our Ruby project page has also been updated to reflect the current status of the different ruby implementations in Gentoo.