I never understood why you would use YAML for storing settings. In fact, I observed that because of YAML devs are less likely to extract things into configuration settings, especially adding a setting seems to involve a manual server restart. I wrote a gem that's IMO much better:

https://github.com/jaroslawr/dynamic_configuration

Settings are configured in Ruby, split into separate files/groups, are easily overwritten per-Rails-env and per-particular-installation, in development environment they are reloaded automatically after a setting is added etc.