Current ruby upgrade from 2.0 to 2.1 reveal at least one issue with dependencies: vim wasn't automatically rebuilt, and neither ruby ebuild nor news warn about it should be done after ruby upgrade.
To reproduce this issue:
- eselect ruby set ruby20
- USE=ruby emerge vim
- install some vim-ruby plugin like Command-T
- try to use Command-T within vim: it should work
- eselect ruby set ruby21
- recompile Command-T with current ruby
- try to use Command-T within vim: you'll get "vim should be compiled with ruby support" error, which can be solved by re-emerge vim
Maybe there are other packages which should be rebuilt after ruby upgrade, I didn't check and just in case rebuild everything listed by `equery depends ruby`.