I''ve just attached a patch to Ticket #340 (YAML, ActiveRecord Serialize and Date formats problem) The bug manifests when you set a value for Date::DATE_FORMATS [:default]. This affects the default Date.to_s behavior, and in most cases will break Date.to_yaml since YAML requires a specific date format. I''m a little unhappy with the approach, since it copies a bit of code from lib/yaml/rubytypes.rb into lib/active_support/core_ext/date/ conversions.rb. I toyed with other approaches that set a temporary Date::DATE_FORMATS[:default] value or defined a temporary singleton to_s method on the Date object before calling to_yaml, but I rejected those approaches because they could fail in multi-threading scenarios (the effects of the "temporary" changes could be seen by other threads). It''d be great if anyone has a better way to resolve this. Thanks -andy