Date::DATE_FORMATS is quite helpful. It lets you do this:
Date.today.to_s(:custom)
with only this code in config/initializers/date_format.rb:
Date::DATE_FORMATS[:custom] = "%Y-%m-%d"
To do the same thing for DateTime instances, like created_at columns, use
Time::DATE_FORMATS.
Time::DATE_FORMATS
To set the default format for either one, set DATE_FORMATS[:default]. This
will cause <%= item.created_at %> to output "2011-08-16", with no extra work
from you.