Symfony date formats are hard coded to the core and the definition is located at lib/symfony/i18n/sfDateFormat.class.php
This is how Symfony handles the date format definitions:
protected $tokens = array( 'G'=>'Era', 'y'=>'year', 'M'=>'mon', 'd'=>'mday', 'h'=>'Hour12', 'H'=>'hours', 'm'=>'minutes', 's'=>'seconds', 'E'=>'wday', 'D'=>'yday', 'F'=>'DayInMonth', 'w'=>'WeekInYear', 'W'=>'WeekInMonth', 'a'=>'AMPM', 'k'=>'HourInDay', 'K'=>'HourInAMPM', 'z'=>'TimeZone' );
And here's the reformating to the Javascript language (used for popup Date plugin)
array('yyyy' => 'Y', 'yy'=>'y', 'MM' => 'm', 'M'=>'m', 'dd'=>'d', 'd'=>'e', 'HH'=>'H', 'H'=>'k', 'hh'=>'I', 'h'=>'l', 'mm'=>'M', 'ss'=>'S', 'a'=>'p')
To change the format of a date for the object_input_date_tag you need to use parameter 'format' ⇒ 'd-M-Y' in the options.
Example:
object_input_date_tag($sklad, 'getCreatedAt', array ( 'rich' => true, 'withtime' => false, 'calendar_button_img' => '/sf/sf_admin/images/date.png', 'control_name' => 'sklad[created_at]', 'format' => 'd-G-yy', ))