code/Debug/Helper/Data.php
public function formatNumber($number, $precision = 2)
    {
        $locale = Mage::app()->getLocale()->getLocale();
        return Zend_Locale_Format::toNumber($number, array('locale' => $locale, 'precision' => $precision));
    }
public function formatNumber($number, $precision = 2)
    {
        $locale = Mage::app()->getLocale()->getLocale();
        return Zend_Locale_Format::toNumber($number, array('locale' => $locale, 'precision' => $precision));
    }
Returns specified number formatted based on current locale

@param     $number
@param int $precision
@return string
@throws Zend_Locale_Exception