Customize exposed views forms

Suppose you want to alter a form you created by using views2 exposed form.
typically, you will get a submit button with the value 'Apply', instead of, for instance, 'Search'.
How to alter this value?

What you need is drupal's hook form_alter.

In your module, create the following function:

function mymodule_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == '?') {
    //what you want to do
  }
}

To know your form_id, just print it:

function mymodule_form_alter(&$form, $form_state, $form_id) {
  var_dump($form_id);
  if ($form_id == '?') {
    //what you want to do
  }
}

Then you will see that, your form_id is views_exposed_form.
That is not only for your exposed view form, but for all exposed view forms.
I think this is a design flaw, because you expect at least your view's name and display type in it.

Anyway, now that we have our form_id, let's do something with our form. We want to alter the submit button's value. But how?
We simply print the form to see where that value is hiding:

function mymodule_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == 'views_exposed_form') {
    var_dump($form);
  }
}

You will get a lot of array values on your screen now, so best is to view the source code of the page (Ctrl+U in firefox).
Searching for the 'submit' button gives:

"submit" ["#value"]=>  string(5) "Apply" 

So all we have to do is

function mymodule_form_alter(&$form, $form_state, $form_id) {
  if ($form_id == 'views_exposed_form') {
    $form['submit']['#value'] = t('Search');
  }
}

And we're done!