class BigDecimal

def to_yaml(opts = {})

Note that reconstituting YAML floats to native floats may lose precision.

This is better than self.to_f.to_s since it doesn't lose precision.
This emits the number without any scientific notation. 
def to_yaml(opts = {})
  return super if defined?(YAML::ENGINE) && !YAML::ENGINE.syck?
  YAML.quick_emit(nil, opts) do |out|
    string = to_s
    out.scalar(YAML_TAG, YAML_MAPPING[string] || string, :plain)
  end
end