$form_state['values'] empty

This thread is to post a solution, rather than ask a question, in case someone else has the same problem.

$form_state['values'] was empty for me in my submission callback. If I set a default value, the default value was shown as the value, otherwise it was empty.

The problem was as follows. First, my code:

/**
 * hook_menu()
**/
function my_module_menu()
{
  $menu['my_form'] = array
  (
    'title' => 'My form',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('my_page_callback'),
    'access callback' => TRUE,
  );
  return $menu;
}

function my_page_callback()
{
  return drupal_get_form('my_form');
}

function my_form($form, &$form_state)
{
  // form definition here
}

If you look closely, i am setting the page callback in hook_form to drupal_get_form(), but my page callback function is not a form definition, rather it calls drupal_get_form() itself. This doubling up of drupal_get_form() is what was causing my troubles. Using the following fixed the problem:

/**
 * hook_menu()
**/
function my_module_menu()
{
  $menu['my_form'] = array
  (
    'title' => 'My form',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('my_form'),
    'access callback' => TRUE,
  );
  return $menu;
}

function my_form($form, &$form_state)
{
  // form definition here
}

Hopefully this can help someone else if they are having the same issue.