Thought you might want to include the following :with_thousands_separator rule in the format method:

if rules.include?(:with_currency)
  formatted << " "
  formatted << '<span class="currency">' if rules.include?(:html)
  formatted << currency
  formatted << '</span>' if rules.include?(:html)
end

if rules.include?(:with_thousands_separator)

formatted = formatted.gsub(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1,")

end

formatted

... borrowed from: http://snippets.dzone.com/posts/show/693

Thanks for clarifying the include.

Cheers...