The stock version that comes with OS X 10.10 DP1 is know to to suffer following errors:
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/yaml.rb:4:in `<top (required)>':
It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- psych (LoadError)
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/yaml.rb:5:in `<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'