Yes, YAML is very nice. Importantly, it reduces to key:value for the 90% of config files that don't require any hierarchy while still allowing hierarchy if you

Yes, YAML is very nice. Importantly, it reduces to key:value for the 90% of config files that don't require any hierarchy while still allowing hierarchy if you need it. I'm not sure I buy the serialization argument, though: it's a human-readable serialization format. One of the big advantages of human-readable formats is that you can craft data objects by hand (for automated tests, initial bootstrapping, etc). Comments are very helpful for those situations.