How to load category (selected id's) in observer

Question

In my observer, i need to load my selected category id's & selected website,

workout:

$category_products  = Mage::getModel('catalog/category')
    ->addAttributeToFilter('category_id', array('in' => array('680','894','895')))
   ->setWebsiteId(2);               // load website id  

If i compare with my cart,

$cart_qty = (int) Mage::getModel('checkout/cart')->getQuote()->getItemQty(); //get cart in observer

observer not triggered.