Very useful

// Minimalistic Event Manager
function my_mem_settings() {
  mem_plugin_settings( array( 'page' ), 'alpha' );
}
add_action( 'mem_init', 'my_mem_settings' );

/**
Find Date in a String

    01/01/2012 will return > 01-01-2012
    30-12-11 will return > 30-12-2011
    1 2 1985 will return > 01-02-1985
    10.12.1850 will return > 10-12-1850
    5 12 85 will return > 05-12-1985
    5 October 2012 will return > 02-10-2012
    MAY 5th 1985 will return > 05-05-1985
    1st March 81 will return > 01-03-1981

*/
function find_date( $string ) {

        //Define month name:
        $month_names = array(
                "january",
                "february",
                "march",
                "april",
                "may",
                "june",
                "july",
                "august",
                "september",
                "october",
                "november",
                "december"
        );

        $month_names_short = array(
                "jan",
                "feb",
                "mar",
                "apr",
                "may",
                "jun",
                "jul",
                "aug",
                "sep",
                "oct",
                "nov",
                "dec"
        );

        $month_number=$month=$matches_year=$year=$matches_month_number=$matches_month_word=$matches_day_number="";

        //Match dates: 01/01/2012 or 30-12-11 or 1 2 1985
        preg_match( '/([0-9]?[0-9])[\.|\-|\/| ]([0-1]?[0-9])[\.|\-|\/| ]([0-9]{2,4})/', $string, $matches );
        if ( $matches ) {
                if ( $matches[1] )
                        $day = $matches[1];

                if ( $matches[2] )
                        $month = $matches[2];

                if ( $matches[3] )
                        $year = $matches[3];
        }

        if ( empty( $month ) ) {
			$s = " ".$string." ";
			$s = str_replace(array('.', ',', ';'), " ", $s);
			//Match month name:
			preg_match( '/(' . implode( '|', $month_names ) . ')/i', $s, $matches_month_word );

			if ( $matches_month_word ) {
					if ( $matches_month_word[1] )
							$month = array_search( strtolower( $matches_month_word[1] ), $month_names ) + 1;
			}

			//Match short month name:
			preg_match( '/(' . implode( '|', $month_names_short ) . ')/i', $s, $matches_month_word );

			if ( $matches_month_word ) {
					if ( $matches_month_word[1] )
							$month = array_search( strtolower( $matches_month_word[1] ), $month_names_short ) + 1;
			}
		}

        //Match 5th 1st 7, day:
        preg_match( '/([0-9]?[0-9])(st|nd|th|,)/', $string, $matches_day );
        if ( $matches_day ) {
                if ( $matches_day[1] )
                        $day = $matches_day[1];
        }

        //Match Year if not already setted:
        if ( empty( $year ) ) {
                preg_match( '/[0-9]{4}/', $string, $matches_year );
                if ( $matches_year[0] )
                        $year = $matches_year[0];
        }
        if ( ! empty ( $day ) && ! empty ( $month ) && empty( $year ) ) {
                preg_match( '/[0-9]{2}/', $string, $matches_year );
                if ( $matches_year[0] )
                        $year = $matches_year[0];
        }

        //Check year:
        if ( 2 == strlen( $year ) && $year > 20 )
                $year = '19' . $year;
        else if ( 2 == strlen( $year ) && $year < 20 )
                $year = '20' . $year;

        $date = array(
                'year'  => $year,
                'month' => $month,
                'day'   => $day
        );

        //Return today if nothing is found
        if ( empty( $year ) || empty( $month ) || empty( $day ) )
                return time();
        else
                return mktime(0, 0, 0, $month, $day, $year);
}

function sort_dates(&$dates) {
	if (!is_array($dates)) return false;
	foreach ($dates as &$val) {
		$sortkey = date('Y.m.d', find_date($val));
		$val = $sortkey.' '.$val;
	}
	sort($dates);
	$left = strlen($sortkey)+1;
	foreach ($dates as &$val) {
		$val = substr($val, $left);
	}
	return $true;
}

/*
Add this handy shortcode

[mem-this-dates] = List dates for this post (start + all repeats)
[mem-this-dates seperator=" & "] = same, but put & between (default = <br/>)
[mem-this-dates id=117 seperator=" & "] = same, but for post ID number 117
[mem-this-dates max=3] = List max 3 dates
*/
function mem_list_dates_function($atts, $content = null) {
	extract(shortcode_atts(array(
		'seperator' => '<br/>',
		'id' => -1,
		'max' => 99
	), $atts));
	if ($id < 0) $id = get_the_ID();

	$mem_start_date = get_post_meta($id, '_mem_start_date', true);
	if ($mem_start_date == "" ) {
		$s = "Please ask us ";
	} else {
		$mem_repeat_date = get_post_meta($id, '_mem_repeat_date', false);
		$mem_repeat_date[] = $mem_start_date;
		sort_dates($mem_repeat_date);
		$s = "";
		foreach ($mem_repeat_date as $val) {
			if ($max > 0) {
				if ($s) $s .= $seperator;
				$s .= $val;
				$max -= 1;
			}
		}
	}
	return $s;
}
add_shortcode('mem-list-dates', 'mem_list_dates_function');