How do you increase the maximum length for labels?

+1

I will also like to know. Each field (in a CMS) whether in core or contributed needs to have a min and max possible values which can be set by the super Admin.

The size of the field labels is limited by the size of the database column that is used to store its value, which is varchar(255). See table {content_node_field_instance}.

Ideal will be admin interface that lets min and max possible values to be set by the super Admin. This should in fact be a core feature of a good CMS.

Dirty hack will be - open your page.tpl.php in your theme folder in a text editor, and
Before this
print $content;
add
$content = str_replace("maxlength=\"128\"", "maxlength=\"250\"", $content);

There is surely a validation function that checks the length of the used labels.

The code that does that seems to be in includes/form.inc

       // Verify that the value is not longer than #maxlength.
      if (isset($elements['#maxlength']) && drupal_strlen($elements['#value']) > $elements['#maxlength']) {
        form_error($elements, $t('!name cannot be longer than %max characters but is currently %length characters long.', array('!name' => empty($elements['#title']) ? $elements['#parents'][0] : $elements['#title'], '%max' => $elements['#maxlength'], '%length' => drupal_strlen($elements['#value']))));
      } 

So, one way to dirty-fix that (no idea of the consequences, whether it will break security and/or site, and perhaps need back-up or keeping the file still open in text editor and undo in case of problem) will be
comment that so it is not executed

       // Verify that the value is not longer than #maxlength.
   /*   if (isset($elements['#maxlength']) && drupal_strlen($elements['#value']) > $elements['#maxlength']) {
        form_error($elements, $t('!name cannot be longer than %max characters but is currently %length characters long.', array('!name' => empty($elements['#title']) ? $elements['#parents'][0] : $elements['#title'], '%max' => $elements['#maxlength'], '%length' => drupal_strlen($elements['#value']))));
      } */ 

As I said before this needs to be an administrative interface feature of a CMS that really allows me to 'manage' my content - so best thing will be to submit an usability issue request at the issues lists of project Drupal.

The great thing inDrupal is that you do not need to hack here and there to do almost anything. You just need to find the hook that suits your needs better.

In this case, use hook_form_alter() for this purpose.

@justclint: It doesn't seem you are looking into the directory of CCK, as CCK doesn't have those files.
What is the not correct in your code is that you are using for the field ID the form ID; it's improbable that both the ID use the same value. Also, the code should just change the value of the array index #maxlength, not all the form field array.

I suggest you to ask for help in IRC.

If you want labels longer than 255, you could use the 255 to store a shortened identifier, and use a custom table, or variable_set, to store a corresponding longer replacement value that you can substitute back in with hooks.

Does this work for Drupal 7?

Neojohan... did you get this to work in D7?

The module does not work for D7.
Does anyone have any suggestion?

Drupal 7 separate issue:
#1645368: How do you increase the maximum length for labels in Drupal 7?

New module:
http://drupal.org/project/remove_field_label_length_limit

Too bad it takes a module to fix this, but this worked perfectly for me.
Thanks.

Is there a better solution to this?

fixed - https://drupal.org/project/remove_field_label_length_limit

For drupal 6 users

Use this in form alter don't touch the drupal core. you can use this globally in form alter to change the form alter if you need on particular form use that conditionally

$form['label']['#maxlength'] = 255;

#17 worked plenty fine for us in D6.