Rails Template: Create a Twitter Application in Seconds(intridea.com)

    function twitterize_text($raw_text) {
      $output = $raw_text;

      // parse urls
      $pattern = '/([A-Za-z]+:\/\/[A-Za-z0-9-_]+\.[A-Za-z0-9-_:%&\?\/.=]+)/i';
      $replacement = '<a href="$1">$1</a>';
      $output = preg_replace($pattern, $replacement, $output);

      // parse usernames
      $pattern = '/[@]+([A-Za-z0-9-_]+)/';
      $replacement = '@<a href="http://twitter.com/$1">$1</a>';
      $output = preg_replace($pattern, $replacement, $output);

      // parse hashtags
      $pattern = '/[#]+([A-Za-z0-9-_]+)/';
      $replacement = '#<a href="http://search.twitter.com/search?q=%23$1">$1</a>';
      $output = preg_replace($pattern, $replacement, $output);

      return $output;
    }