Example for make blocks easily configurable for webmaster without 'administer blocks' access (and without huge permissive module). This fully use formapi (http://api.drupal.org/node/15320) and custom code.

blockadmin_example.admin.inc

<?php

function blockadmin_example_admin() {
  $text = variable_get('blockadmin_example_page_text', array('format'=> 'filtered_html', 'value'=> ""));

  $form['blockadmin_example_page_text'] = array(
    '#type' => 'text_format',
    '#format' => $text['format'],
    '#title' => t('Texte'),
    '#default_value' => $text['value'],
    '#size' => 20,
    '#required' => FALSE,
  );

  return system_settings_form($form);
}

blockadmin_example.blocks.inc

<?php

/**
 * Implements hook_block_info().
 */
function blockadmin_example_block_info() {

  $blocks['myblock'] = array(
    'info' => t('Block with admin content'),
    'cache' => DRUPAL_CACHE_PER_PAGE
  );

  return $blocks;
}

/**
 * Implements hook_block_view().
 */
function blockadmin_example_block_view($delta = '') {

  $block = array();
  switch ($delta) {
    case 'myblock':
      $block['subject'] = '';
      $block['content'] = _blockadmin_example_block_myblock();
      $block['class'] = array('blockadmin-example-myblock');
      break;
  }
  return $block;
}

/**
 * Generate content for myblock block
 */
function _blockadmin_example_block_myblock() {
  $content = variable_get('blockadmin_example_page_text', array('format'=> 'filtered_html', 'value'=> ""));
  return array(
    '#markup' => check_markup($content['value'], $content['format'])
  );
}

blockadmin_example.module

<?php

module_load_include('inc', 'blockadmin_example', 'blockadmin_example.blocks');

/**
 * Implements hook_menu().
 */
function blockadmin_example_menu() {

  /*
  * **
  * Administration
  * **
  */
  $items['admin/blockadmin'] = array(
    'title' => '[Name site] administration',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('blockadmin_example_admin'),
    'file' => 'blockadmin_example.admin.inc',
    'access arguments' => array('administer blockadmin_example page'),
    'type' => MENU_NORMAL_ITEM,
    'weight' => -1
  );
  $items['admin/bn/blockadmin_example'] = array(
    'title' => 'Example block',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -1,
    'access arguments' => array('administer blockadmin_example page')
  );

  return $items;
}


/**
 * Implements hook_permission().
 */
function blockadmin_example_permission() {
  return array(
    'administer blockadmin_example page' => array(
      'title' => "Administrer Blockadmin Example Admin Page",
    ),
  );
} // blockadmin_example_permission